The Bat Signal is a hand gesture consisting of the pointer finger on one hand and a hole made with the opposite hand while moving the index in and out simulating a sex act.
A girl asks a friend of hers how she should let a guy know she wants to take him home. Her said says "give him the bat signal".
Two male friends are at a bar, one friend asks the other "how can I find out if she'll put out without directly asking her"? His friend replies "give her the bat signal, you'll have your answer after that".
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