Riddle Me This!

I was sad to hear that the incomparable Frank Gorshin, a.k.a. "The Riddler", died this week from lung cancer and emphysema. Batman was a favorite program of mine while I was growing up, and the Riddler was one of my heroes.

In honor of Frank Gorshin, I leave you with a riddle from the series: "What has yellow skin and writes?" Answer in the comments section.