I have used Nail polish, but like it was said in a prior post, you will have to be SUPER careful in using it. I have used it on a few phones and havent damaged the the OEM face plates on most phones, since the plastic itself is colored and not painted. However, the cheap face plates are painted and will rub off.
I use just a dab on a qtip, brushing just the logo and being very careful...never had a problem.