If you are talking about the flying creature that lives in caves (and elsewhere), read on:
The general sign for bat shows how bats like to sleep with their wings
folded over their chests while hanging upside down.
(660KB .gif file. Suggestion: After clicking, switch back to main window and browse while waiting for the new secondary window to download the animation.)
You can use the sign for "flying" (flapping wings) to represent a bat.
(197 KB .gif file)
Some people use the sign for "vampire" to mean "bat." A group of Deaf Teenagers used to sign "VAMPIRE" + "MAN" to mean "Batman."
(85KB .gif file)
American Sign Language University ™ ASL resources by Lifeprint.com © Dr. William Vicars