To sign "boy" in American Sign Language (ASL), there are a few different options:

• Bring your fingers and thumb together then apart in front of your forehead, as if grasping and releasing the tip of a baseball hat.
• Grab the brim of an imaginary baseball cap sticking out from your forehead area.
• Tap the fingertips of your dominant "flat O" handshape twice in front of you with your thumb, with your palm orientation facing the left side if right-handed.

Its important to note that the sign for "boy" is often used to mean "male" in general, and can also be used to mean "guy" or "man".