What can you write on mirrors with that will come off?
write it on the mirror with a white-board (dry erase) marker. The marker will come off with a swipe of a kleenex or washcloth, and you'll be relatively certain they saw the note.
How do you write on a mirror?
Use white board markers in a dark color such as black to write inspiring messages on mirrors in your home. You can then use an eraser to change the messages each day or each week.