My sign would read, "Wait! Did you remember to write your name on your paper? Highlight it with a yellow highlighter or write it in using a highlighter that is NOT yellow!", and there would not be a sign on my highlighter container.
Outlaw "I'm Done!" I LOVE this post from Kady at The Teacher Trap. She makes some really good points and includes suggestions for helping kids change their mindsets about rushing through their assignments.