Allow full alphabet on the roof of government worker vehicles

Description: To allow full A-Z on top of government vehicles that already allow call signs on them.

Reason: EMS have call signs that follow the [letter-xx] format. We can add A-00 ontop of our command vehicles but no other letter and would like to request other letters to be available too, even if it's just in the1st slot.

Our Supervisors were recently assigned a Scout to use on duty and they are permitted to add their callsigns [B-00] ontop. But because B-Z aren't an option, they can't.