I don't think it has to do with RULES, but rather manufacturere safety guidelines.
The Sparco suit I just got came with a book that has a section about this.
NO IRON ON - Ironing a fire suit will damage it's fire resistance.
Sewn on patchs must be sewn on with fire retardant thread, and the back of the patch SHOULD also be fire retardant. Futhermore, it is only to be sewn into the outer most layer of the suit.
In my opinion, totally NOT worth it. Make some t-shirts for crew to wear, leave the fire suit alone. It's life support / saftey equipment.... don't mess with it. Since I have a black suit, I got a RAD reflective orange safety vest for when out of the car at night. I think I might make it like a boyscout vest and put the necessary logos on it instead.
(I'm just a rookie though, what the hell do I know?)
