The signature system is used for keeping track of a player's current stats, inventory etc. Player's are asked to leave this right alone. If players are caught tampering with this there will be consequences.
Players are also asked to turn off their signature when posting out of character. This can be done by un-selecting the 'Enable signature?' box beneath the 'Enter your Post' section, as the signatures take up a lot of space and are only to be used for missions.