I needed to attach a mirror to the back of a door and wanted to use damage-free mounts. The adhesive on the 3M Command strips peeled off the paper backing on the mirror (cheap mirror bought at Walmart). I created this design to give a solid surface to attach the command strip. Modeled it to match the style of my mirror as best as I could with limited experience. Printed four of these, two of which were mirrored in my slicer. I used the large picture hanging strips, example here: https://a.co/d/hxbExwo (not an affiliate link). Seemed to work fine (probably way overkill) for my lightweight mirror but YMMV and I make no promises as to the performance of either the clip itself or the adhesive. 

I printed this with the back-side on the print bed for better layer adhesion and top layer aesthetic quality. I used organic (tree) supports everywhere. They took a couple minutes each to remove with a decently-tuned slicer profile, but not too difficult. Using organic supports only on build plate could be feasible, or you could print it oriented with the short side on the build plate with no supports if you're comfortable with the layer adhesion and surface quality.

Included Fusion 360 file for easy modification.