Ahh, yes, vampires.
I came up with this sort of randomness while I was at work. It isn't finished, and it is only a suggestion. If it is a suggestion...
The Blood Oath of the Vampires
To keep the Blood safe, even above ones own personal safety.
(Translation: A vampire must keep the entire culture of vampires a secret at all costs, even their own death.)
To never take more blood than is needed.
(To not kill more people for blood than necessary, and than you can drink)
...And that is it so far. It is the oath all vampires enter into once they are turned into a vampire, whether they know it or not. You can add to it, or just reject it completely.