HANG-UP: The
American Sign Language (ASL) sign for "hang-up"
The right sign for "hang up" depends on your meaning.
If you mean "hang up" as in hang up a clothes hanger on a rod or to put
something onto a peg use this version of hang up:

To hang up a phone you mime the action.
Traditionally it was:
These days with a smart phone if you have a lot of context you can depict
clicking the hang up button:
and maybe mime putting it in your pocket or purse or wherever you keep it.
Those of us who use a remote controller and a video phone sometimes hang up like this:
Or to make the hang up concept very clear you can sign "click on, disconnect":
Another sign that works quite well is the one-handed "OFF, shut down, power off,
closed out" sign.
See:
p.s. Those of us who used TTY's (teletypewriters / later called TDD's by some people) would mime the act of taking the phone handset out of the TTY cradle and putting it back onto the phone cradle. There were also the type of TTY's that we plugged the phone jack directly into the TTY. I don't recall signing hang-up for that type. Just signing "FINISH" or "disconnect," (Or, heh SKSK). SK was shorthand for "stop keying."
Notes: See: PHONE
Notes: