M-9

From Memory Alpha, the free Star Trek reference

M-9 was a designation of gestural language learned by Lt. Commander Data in his attempt to communicate with Riva, a deaf mediator from Ramatis III. (TNG: "Loud As A Whisper")

One of the gestures of the M-9 sign language was similar to the Vulcan salute.

According to the Star Trek Encyclopedia, most of the gestures seen on Data's screen were adapted from American Sign Language. The Vulcan salute was included "to see if anyone would notice."