UDID
The UDID, ID or Urban Dead ID is a number identifying a character in Urban Dead. It, along with the character's name, is a unique identifier, allowing the character to be identified from it. It can be used for certain actions via "question marks", such as, and most generally, profile links.
When discussing a third party, such as calling out a player killer on the radio or tagging a revive point with a do not revive message, players will often include the UDID of the character in question. This might be written out like "Kevan (id=14) sighted!". Including the UDID gives others the opportunity to add the subject to their contacts list for future reference.
Previously, if you knew a character's name and needed to know their UDID, the Urban Dead Profile Database provided a database of all characters in the game, allowing you to search by name and providing the profile(s) link(s) to match. That service is no longer available.