There is no widely used or recognized
sign for asterisk.
One strategy for indicating an asterisk would be be to draw an asterisk in the
air using your index finger.
ASTERISK:
Note: Another approach to conveying
the meaning of "asterisk" would be to use the sign "STAR."
The context of your conversation would influence the interpretation of the sign.
For example, if you were discussing typography or fonts and you did the sign for
"STAR" the other person would assume you were referring to an asterisk, (not a
distant sun).
See: "STAR"
You can learn sign language online at American
Sign Language
(ASL) University (tm)
Sign language lessons and resources. Dr. William Vicars (c) Lifeprint.com