These are mirror hooks.....
Topzone® 1/4" inch Heavy Duty 25 Pound Crystal Clear Plastic Mirror Holder Clips, Pack of 12 Pieces - - Amazon.com
I recommend these as a safety back up, as there is really no way of checking/inspecting how well the mirror adhesive was installed without risking breakage of the mirror. Mirrors are glued on to the drywall with special mirror adhesive. It usually works well. On rare occasions a mirror can fall, and of course that can be very dangerous.
Adding these mirror holders is cheap insurance, provided they are installed properly into studs with good screws.
Understand that everything has a failure rate. Most failure rates are very small. I have no way of knowing the failure rate here on mirror adhesive, but if there are around 75,000 homes here, each with at least 2 bathroom mirrors, that is over 150,000 mirrors. If one percent fail, that would be 1,500 mirrors......001% would be 15 mirrors.
The failure rate of me driving through a roundabout is much higher.
I have also seen some nice retrofit framing put around these mirrors. It really gives a different look and would also hold the mirror...
Frank