SECRET: The American Sign Language (ASL) sign for "secret"

The sign for "SECRET" is also used to mean "PRIVATE."

The location and handshape of the sign 'secret' when produced with different movements and non-manual markers (facial expressions) can mean "SUFFER" or "PATIENCE."

SECRET:
Tap your lips twice with the back of the "A" hand thumb.

If you mean 'secret' as in "keep a secret, you are not telling the secret" you would sign:

Another version of "I'm not telling:"

Sample sentence: It is impossible for my sister to keep a secret.

Notes: 

Also see: SUFFER

Also see: PATIENCE

Also see: PRIVATE