to identify a vampire, look for:
no hunger or thirst
lock a suspected vampire in a room, normal dwarfs get hungry/thirsty/tired, vampires do not, if you lock someone in for a year, and they dont die of thirst or starvation, then this is your final confirmation that you have caught a vampire
(make sure to let innocents out when they approach dehydration/starvation
white hair
(i hear vampires always have white hair, and only vampires have white hair, not sure on this, though)
long lists of absent relatives, or previous forts
(i had a few with a LIST 17 lines of text long, just names, that's a dead giveaway)
vampires never mention thoughts of food or sleep
(they do mention beds they own, just specifically they don't mention sleeping)
items of human/elf/dwarf bone,
"it's normal for people to have jewelry Urist, but i dont think those dwarf bone earrings count under normal"
looking different from stated age
the "has the appearance of a x year old person" line also i believe only happens for vampires
vampires can be specific curses, if you want to read a lot of lore generated on your map
vampires always use aliases
these are not the same in all lists of names, if you suspect someone, look for them in lists, like the job list, the citizen list, and assigning a tomb list,, normal people vill show up in all three, if someone is missing from one of those lists, that's a sign you should check further
(i dont know if this has been changed recently, but this worked in 34.02)
did i forget anything?
edit: can you tell i had a world with like 20% vampires in the population at some point?