Will sharpie stay on the back of my LG G5?

Just try it. Sharpies aren't really "permanent"... the ink can be removed with alcohol... especially on hard surfaces.

I should also state though that on cloth/leather/porous material it's tougher to get out... sometimes impossible unless they fade.
 
Alright thanks man. I didn't know it could be removed with alcohol if it doesn't rub off first.

I used to work in a jewelry store and learned that using perfume or cologne can remove glue and marker stains better than just straight alcohol or anything else for that matter. It has an intense concentration of alcohol. It's pretty neat how easy it works. Try it on your skin. Use a sharpie on your arm, then spray cologne, it literally runs off your arm.

P.S. Just noticed I awake this post from the dead.