How Can I Catch a Thief with skin color changing ingredients?

I remember an old episode of M.A.S.H. where Hawkeye caught a thief by 'saying' that he put something on the items in question that would change the color of the thief's skin. Does anyone know of an easily obtainable ingredient that will do this so I can catch a thief? I need something that I could put on a doorknob at night and wipe off when not needed. Thanks in advance.How Can I Catch a Thief with skin color changing ingredients?
Silver Nitrate works really well. Just takes a little and will turn your skin black. If you're in school, most chemistry labs have this.How Can I Catch a Thief with skin color changing ingredients?
use iodine. it's easy to get and will stain the skin for a few days.