You can go with anything here.  Images, words, etc.  For a kids bathroom maybe “Floss and Brush”.  Designing a little kids room maybe a fairy picture or dinosaurs.  Motivational words, mandalas, a favorite pet.

I went with “you are amazing” but if I did it again I would change it to “you look amazing” since this is going in a guest bathroom.

Pick how large you want the size to be on your mirror.  

We are limited in size we can do at once so you'll need to break up your words or images into pieces that can fit on the canvas.  I changed the colors here to make it easier to see.

Once we break it up we'll want to keep it straight so I added a rectangle that can be used for framing against a tape line later.

Don't forget to mirror your text!

This will be engraved from the back so we need to mirror it when engraving so it shows up correctly.

Line everything up with your rectangle.

My mirror had a paper backing so I needed to cut it open to get to the mirror.  Make sure you don't scratch the backing in the process.

The painter's tape helps to keep a good straight line.

Check, check, and recheck your placements.  It's in mirror image so it can be harder to tell and you don't want to accidently switch them around.

You may need multiple passes to get all the way through the backing.  I used a flashlight from underneath to be able to see through the glass to see if I got it all.  Repeat as many times as needed and make sure that there is something underneath to catch any burn through.

Spray the back side of the mirror with spray paint.  

You can go with any color you like here so have a little fun.

Some people choose not to paint it and add back lighting instead which can also be a cool choice but I wanted something simple for the bathroom that won't be immediately noticed.  It makes it a little more fun when they find it.