I grew up in a body shop, and had my own for many years.
+1 for Imron, used it extensively in the automotive world, and in this industry, for sign faces, frames, poles, whatever, it can't be beat, plus they can match corporate colors. It's glossy without clear coat, catalyzed for hardness, and way more scratch resistant than any rattle rocket, enamel, or latex, and gives probably the best UV and weather resistance of all single stage finishes. They still need time to cure, at the body shop we used to just park cars out in the sun for a day or three before putting any graphics, stripes, or emblems on them after painting, and never had any issues. It is more costly than other brands, but it's not the kind of stuff you keep a stock of, only buy what's needed, when it's needed. In a sign shop, unless you're finishing hundreds of panels, you'll probably never buy anything larger than quart, or even pints if your vendor will mix it for you, it goes a long way compared to other paints. Catalyst comes in pints & quarts, the only thing you'll need in a gallon quantity would probably be thinner to clean paint guns, so you can get by with a small flammable cabinet for everything to appease the fire inspector.