Here is a good general sign for "skateboard."
It is based on the concept of four wheels.
The upside down bent "V" handshapes represent two-wheels each.
You do a double forward movement. (You move forward about 10 centimeters, back 8 centimeters, and forward 10 centimeters).
SKATEBOARD (or "skateboarding")
Animation: "skateboard"
Notes:
There are other signs for "skateboarding" out there.
For example, one version uses the non-dominant palm-down flat-hand to represent the skateboard and puts the index finger of your dominant upside-down "V" hand on the "skateboard" to represent a person "on the skate board." Then you move the middle finger as if it were a leg and foot "pushing" your skateboard forward. It is a pretty clever little sign but doesn't feel quite as natural as the version above.
See: ICE-SKATE
See: "SKATING"
See: "SNOWBOARDING"
Notes: