There is no one "perfect" sign for "pacifier." In general you are going to have to mime the action of putting one into your mouth using either an "x" handshape or a loose "G" handshape. Or you can tap your lips twice with the front knuckle of the X-hand.
PACIFIER (version 1)
Use an "x" hand or a modified X hand:
There is another version that uses a loose "G" hanndshape.
Notes: