Hold up your non-dominant hand in a modified "four" handshape, (the thumb
is alongside, not across the palm). Hold your dominant hand about five
inches away from your non-dominant hand. (The dominant hand is between your
non-dominant hand and your chest or face.) Then quickly move your
dominant hand forward until it smacks into your non-dominant hand.
JAIL or PRISON:
Another version of this sign that I tend to see used more for jail uses "V"
JAIL or PRISON (version)
You might see this version too. For this version the dominant "V" hand moves quickly forward and down slightly until the
back of the index and middle fingers slap against the front of the
index and middle fingers. The dominant hand keeps moving forward and down past
the non-dominant hand. I see this version used somewhat more
as a verb. ("To be thrown in jail!)