Serials are used by MTA to identify players, serials are bound to your hardware configuration and your MTA community account.
Serials can contain numbers and letters, the format:
[n]
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Server administrators can ban the serial, this is useful for players who have a dynamic IP.
From MTA 1.0 players can login ingame with the MTA community account.
You shouldn't rely entirely on serials to identify players - serials may be able to be faked and it is not guaranteed that two players will not have the same serial (though this is unlikely).
