Put this in your server resources, start it and join your server, next check the server console/logs.
whatsmyid.zip (715 Bytes)
Output should look something like this: (depending on how many identifiers are available/being used, you might see more/less identifiers after your name.)
Player: Vespura, Identifier #1: steam:1100001059
Player: Vespura, Identifier #2: license:4510587c13e0b645eb8d24bc104601
Player: Vespura, Identifier #3: ip:127.0.0.1