If a vampire drains a victim completely of blood, would they show any bruises? If not, what other trauma would they show?
Given that a bruise is, literally, a sub-dermal hemorrhage… I’d be willing to go out on a limb and say, probably not. Actually, if you want something sufficiently messed up; a vampire that preferentially goes after bruises is a possibility.
That said, corpses don’t generally bruise. So, if they were killed, then exsanguinated, there wouldn’t be any bruising. Depending on how fast the vampire was draining them, I’m not even sure if bruises would form.
Now, what would happen if you hooked a vacuum cleaner up to someone’s vascular system? Yeah, I don’t know, and I really don’t want to research that. (Mostly, because I know it’s been done, and will return valid information.) But, depending on the specifics of how vampires work in your setting, they could actually rip apart the victim’s circulatory system, resulting in massive hemorrhaging, or collapsed veins and arteries.
Of course, if your vampires are messy eaters, and literally rip their victims apart… you’d see that on the victim.
This kind of illustrates the problem with vampire questions in general. There isn’t much consistency. Either in fiction or folklore. Most societies have some kind of vampire myth. It builds out of cultural anxieties, usually in reference to death and handling the dead. Though, it’s probably worth pointing out that Dracula, and the modern vampire mythos spawned from him has a lot more to do with sex, sexuality, and xenophobia, than anything to do with funerary rituals being botched.
The result is that vampires are as varied as the human cultures that created them. So, asking, “how would they work?” Is going to result in a fair bit of guess work. The other side of this is, in using them, you have a lot of freedom to decide how the rules work for your vampires.
In the past I’ve identified Ravenous (1999) as a pretty fantastic vampire movie. I stand by that. But, there aren’t any vampires in it. Not explicitly, anyway. It’s about cannibals who are empowered by feeding on human flesh, rejuvenating them and granting superpowers. The movie calls them Wendigo, but, they’re vampires.
For modern settings, I strongly recommend the parasitic variety. In the modern world, dead bodies drained of blood turning up is a clear sign that something has gone horribly wrong, and in a setting where vampires exist, you’re going to have people who hunt them. Meaning an exsanguinated victim is just one undead fashion reject signing themselves up for a world of hurt.
Although it’s a pain to find, I do still strongly recommend the British Ultraviolet TV series. It was a smart look at vampires hiding in the modern world. It’s also a very intelligent, and rational, handling of the pre-millenial anxieties of the late 90s.
White Wolf’s Vampire: The Masquerade is somewhat similar to Ultraviolet. They’re both working towards building vampires that could exist in the modern day. Though, V:TM is a lot less shy about insinuating vampires into social systems like the Police and government, while Ultraviolet is more interested in the vampire hunters. I did a full article on White Wolf’s World of Darkness setting last year. So, that might be worth skimming before jumping after them. But, for writing horror, it is a very good reference to look at and think about.