This is a general-purpose L bracket from 3 Legged Thing, best known as makers of tripods named after people for no apparent reason. This thing probably had a name too, like "Elizabeth" or "Fitzwilliam" or something, but they don't make it any more, so we may never know. It's a good little bracket, though, with a rubberized mounting surface and a movable fixing screw. There are Arca-style clamping surfaces on both axes, a pair of strap loops, and a bright orange anodized surface.