Shadowmarks

Shadowmarks are symbols used by the Thieves Guild, so that buildings throughout Skyrim can quickly be identified by Guild members as to their potential usage. The symbols are usually carved next to the building's doorway.

Dawnstar

 * There are no confirmed Shadowmarks in Dawnstar.

Falkreath

 * There are no confirmed Shadowmarks in Falkreath.

Markarth

 * Silver Blood Inn has a "Danger" sign on the upper right side of the doorway.
 * There is a "Loot" symbol high up on the doorway to Arnleif and Sons Trading Company.
 * The Treasury House has the symbol for "Loot" to the left of the doorway.
 * Nepos' House bears the symbol "Loot".
 * The Hag's Cure has the "Loot" mark to the left of the door.
 * "Loot" symbol on Ogmund's House to the left of the door.
 * Endon's House bears the "Fence" symbol and the "Protected" symbol.
 * Smelter Overseer's House has the symbol "Loot".
 * Abandoned House has the "Empty" mark to the left of the door.
 * Vlindrel Hall has a barrel labelled "Thieves Cache" outside the front door, once the Dragonborn has completed the special job for Delvin for the city.
 * The Treasury House has a "Thieves Cache" outside the front door.

Morthal

 * There are no confirmed Shadowmarks in Morthal.

Raven Rock

 * Glover Mallory's House has the "Guild" symbol to the left of the door and a "Theives' Cache" barrel in the basement.

Riften

 * The button to get into The Ratway is a Guild sign.
 * In front of the Black-Briar Manor is the "Protected" sign.
 * In the door frame of the Bee and Barb is the "Loot"sign.
 * In the garden of Honeyside, the house you can purchase, there is a barrel with the "Thieves' Cache" mark on it.
 * The Riftweald Manor has the "Guild" symbol to the left of the door.
 * Snow-Shod Manor has the symbol for "Loot" to the right of the door.
 * Bolli's House has the symbol for "Loot" on the wall.
 * The Scorched Hammer has the "Loot" sign to the right of the door.
 * A "Thieves Cache" is located on the Riften docks in the lower canal section with a "Loot" symbol on it.
 * On the stone step in front of Beggar's Row is the "Empty" sign.
 * Left of the door to Elgrim's Elixirs is the "Loot" sign.
 * Stone Steps in front of Marise Aravel's House and Valindor's House have "Loot" signs.
 * On the wooden support beam to the right of Romlyn Dreth's House is a "Loot" sign.
 * Next to Grelka at the marketplace there is the "Danger" sign.
 * On the left sign of Madesi 's stand, there is a "Loot" sign.
 * On the left side of Aerin's House there is a "Danger" sign.
 * On the stone step to the left, right outside the archway leading to the Ratway is the "guild" sign.
 * On the door frame of The Pawned Prawn is the "Loot" sign.
 * In Riften Jail, on the back wall of the cell the player is placed in, there is an "Escape" sign next to a broken shackle button. (This button may be bugged and only cause guards to run in and attack the player)
 * In Riften Ratway Vaults, on the 2nd floor, there is a "Loot" sign on the wall above a big box.
 * On Brand-Shei 's stand in the marketplace is the "Loot" sign.
 * After going through Mercer Frey's home and underground there is a hole which you must drop down. On the wall on the far side of the hole is an "Danger" sign.
 * In the center of town on the barrel next to Brynjolf's stand there is a "Guild" symbol.

Solitude

 * At the East Empire Company Warehouse, to the right of the entrance is the "Danger" sign.
 * At Erikur's House by the Blue Palace at the left of his side door is a barrel with the "Protected" sign. The other two doors to his house also bear "Protected" signs.
 * Jala's House has an "Empty" mark on a barrel to the right of the door.
 * Addvar's House bears the "Loot" mark on the left hand side of his door.
 * Evette San's House has a "Loot" mark to the right of the door.
 * Vittoria Vici's House bears a "Loot" mark on the door opposite Proudspire Manor but no marks near the other two doors.
 * Behind the above mentioned house is also a "Thief Cache" barrel.
 * The Winking Skeever bears the "Loot" sign to the left of the door.
 * Bits and Pieces has the "Loot" mark to the left of its door.
 * Radiant Raiment bears the symbol for "Loot".
 * There is a "Loot" mark on the column at the top of the staircase facing the Solitude Blacksmith.
 * There is a "Fence" mark to the left of  Gulum-ei in The Winking Skeever.
 * Bug: In the Solitude Jail there is supposed to be a shadowmark in the left back corner (when viewing the door as the front). This marks a one time use hidden exit.

Whiterun

 * At Belethor's General Goods, to the right of the shop door is the "Loot" mark.
 * Arcadia's Cauldron has the "Loot" mark on the right side of the shop door frame.
 * The Bannered Mare has a "Loot" mark low down to the right of the front door.
 * The Guard Barracks has a "Danger" sign, this may be partially obscured by a lavender bush.
 * Amren's House displays the "Danger" sign to the left of his door.
 * Heimskr's, Ysolda's, Olava the Feeble's and Uthgerd 's houses all bear the "Empty" sign.
 * Ysolda's House, right side, there is a chest hidden behind some barrels with the "Thieves' Cache" sign.
 * House Gray-Mane has a "Loot" mark on the door facing Jorrvaskr below the left hand dragon head door post.
 * House Battle-Born has a "Protected" Shadowmark at the bottom left of the door.
 * Carlotta Valentia's house bears the "Loot" symbol to the right of her door.
 * Carlota Valentia's market stall also bears the "Loot" symbol, next to where she sells.
 * Jorrvaskr has the "Danger" symbol on a pillar to the right of the front entrance.
 * Under the bridge just through the main gate is the "Safe" symbol. (However, being in this location will not stop guards from pursuing you nor keep them from attacking you.)
 * Severio Pelagia's House has the "Loot" mark to the right of the door.
 * The House of Clan Battle-Born has the "Protected" mark to the right of the rear entrance.
 * Hall of the Dead has the "Danger" mark on a pillar to the left of the stairs.
 * The Drunken Huntsman has the "Loot" mark to the right of the front entrance. This mark is hidden behind the barrels.
 * Dragonsreach Dungeon has an "Escape Route" mark by each grate within the cells.
 * There is a cache marking on the side of Ysolda's house, the marking and the cache are behind the fallen barrel.
 * There is a danger marking on the right side of the guard house near the entrance to the city.

Windhelm

 * Brunwulf Free-Winter's house bears the "Loot" mark.
 * Belyn Hlaalu's house in the Grey Quarter is marked with the "Loot" symbol.
 * Atheron Residence has the "Loot" mark.
 * House of Clan Cruel-Sea has a "Protected" mark on the upper left of the side doorway.
 * Viola Giordano's House bears the "Loot" mark.
 * House of Clan Shatter-Shield has the mark "Loot" above the door to the right.
 * There is a "Danger" mark located outside the Aretino Residence.
 * On the Blacksmith Quarters, there is a "Loot" mark.
 * Argonian Assemblage bears an "Empty" mark.
 * The altar found in Hjerim during the quest Blood on the Ice has a symbol on it that bears a striking resemblance to the "Danger" symbol.

Falkreath Hold
Pinewatch has a "Danger" sign etched to the lower right of the front door.

The Pale

 * Irkngthand - In the Slave Pens, there is a "Thieves' Cache" mark high up on some pipework near the falmer "village".
 * Irkngthand - There is a "The Guild" mark in the room directly behind where one meets Karliah and Brynjolf. It is located through the doors on the right on top of the table with some lockpicks and a bottle of Black-Briar Reserve.
 * Irkngthand - On a treasure chest in a side room near the end of the Grand Cavern, there is an "Empty" mark. The wall also has a backwards message from Mercer Frey, taunting "one step ahead".

Solstheim

 * Glover Mallory's shop has the "Protected" symbol.

Winterhold Hold

 * There is a "Empty" sign on the guard barracks
 * There is a "Danger" sign on the back of the Jarl's Throne ("tcl" command for computer is required to view).

Whiterun Hold

 * Honningbrew Meadery has the "Fence" mark to the left of the entrance.
 * There is a "Safe" mark under the bridge in front of the main entrance to Whiterun.

Trivia

 * The "protected" Shadow mark does not apply when assigned a Thieves Guild job in that location. (e.g. a Burglary Job assigned by Vex.)
 * Before completing the Under New Management quest the Cache in Solitude which should be somewhere around Proudspire Manor cannot be found.
 * They are a reference to Hobo Sign Code
 * Interestingly, there appears to be 'The Guild' symbol on the cheekguard of the Imperial Helmet.