Q. What does the term "flash" mean again?
A. Comes from the carnival world. It means an attraction, a dazzler, an eyeful designed to catch the "marks" attention as he walks through the state fair, seaport, circus, rodeo or strolls down the carnival midway.
Flash is the bright design, the purple dog on the top shelf, the gleaming bakelight radio in orange, yellow and green, the zip, zap and pop that makes you reach in your wallet, suspend belief and throw as much dough as possible at the booth. In this case, you want the beautiful pin up girl, the brave tiger or the sailing ship memorialized on your person.
Flash is the top shelf. As opposed to "slum" which is the crap in boxes sitting in the dirt by the carneys feet. Slum is comprised of rubber snakes, frog clacker noise makers and those woven Chinese finger traps where the more you pull, the tighter they got. Slum is the red cellophane fish that would curl in your hand. Or not, telling everyone something about your personality.
The term transferred over to the tattoo world. A good and bold sheet of tattoo flash would turn heads and stop 'em in their tracks.