They often work in groups of three and can sometimes appear upon fast traveling to a new location. If the Dragonborn is (or was) a vampire, they will attack them on sight. They will continue to appear, despite the completion of the Dawnguard quest line, showing the continued tensions between the factions.
Dawnguard: "Those vampires put up a hell of a fight. You think they turned him?"
Vanik: "I don't know, maybe. Won't know until we get him out of there."
Dawnguard: "How do we do that?"
Vanik: "I'm working on it, now give me some silence so I can think."
- A named Dawnguard soldier called Saliah can be randomly encountered.