The sign for "thief" is just a combination of STEAL and
PERSON.
THIEF = STEAL + PERSON





You might see some people signing "bandit" to mean "thief." This
sign is based on the idea that the traditional (old time) bandits had
mustaches.
BANDIT:

Here's a version of the sign "GUNS DRAWN" that can be used to mean
""it's a hold up" or "rob." The sign uses modified "H" hands with
the thumbs sticking up.
ROB / "hold up" / mug:

You can learn
American
Sign
Language (ASL) online at American Sign Language University ™
ASL resources by Lifeprint.com © Dr. William Vicars