I installed a mirror and wanted it to be frameless and hidden fixings. I came up with the idea of a hidden french cleat within a sheet of plywood.
Front view, not pretty
Side view, still not that pretty
I drilled two holes at the top so that I could use my jigsaw at an angle to cut the 45° that makes the french cleat. You then fix the square to the wall and then attach the mirror to the big piece and slide it on.
