You are probably talking about a flash bracket.

I'd guess something along the lines of the Stroboframe Camera Flip bracket. The design has been around a long time and the patents have expired, so there are now several competing brands with more-or-less the same design, and Stroboframe's own prices are significantly lower than they were when I bought one back in the '80s for use on my last-resort backup 35mm system for weddings. (The current price is in the $US 40 range; it was more than $US 100 in '87. Adjusted for inflation, it's pretty much free now by comparison.)

Unlike camera-rotation brackets with their large and obvious mechanical arc mechanism, it only has two positions (portrait or landscape) and the mechanism is a whole lot less obvious—just the frame, the L-shaped camera platform, and two solid links between the two that are only really visible during the flip operation. It's also a whole lot less sturdy that the much more expensive arc rotation brackets, but it's not intended to be a tripod head or mounting plate—it's pretty much expected that your hand will be on the camera, even when used on a tripod/monopod.