The sign for "straight" holds a dominant flat hand in front of your face. Fingertips pointing upward. (If you are right handed, the palm will be facing left.)
Move your hand (and arm) forward as you change the orientation of the fingertips to be pointing forward. Quite a bit of the movement is in the wrist.
STRAIGHT:
STRAIGHT: (side view)
Question: Can this sign be used to mean "heterosexual?"
Answer: Yes.
Notes: