Infofields are a means restricted to factions only.
Infofields are explained in The Guide under 'Faction Privileges'.
There had been suggestion threads about the feature that everybody can set his/her own infofield, but they had been shot down.
The answer that was provided was something like "Infofields are a somwhow official title, in case a freelancer wants to name himself a fancy title he can use his signature."
And as nearly always: the search function is your friend :-)