A flasher button may suggest something belonging to an exhibitionist, but it is one of the names given to buttons (i.e. political buttons) that use lenticular photographic layering to flicker (or flash) between two images. (Another term is "Flicker.")

Back in the day, a U.S. presidential campaign was not a campaign without a good supply of lentincular buttons; all parties used them. Sadly, with the rise of stick-on adhesive "buttons," they are no longer the mainstay they once were. The ones shown here, also known as Vari-Vue, produced by Pictorial Productions Inc, of Mt. Vernon, N.Y., who hold the Patent Number 2,815,310, are prized collectibles. This process was also used for countless advertising doodads and often found in boxes of Cracker Jack (when the prizes were good).

A student of mine recently had her business card done the lenticular way, and many 3D lenticular printing companies are accessible online. Here's one and its gallery of effects.