Human beings making up a group.
Writing system: si5s (2013). The main symbol (without the slash) is the same as Japanese character for "people". Did they borrow the character from Japan into ASL writing?
The two bars represent PEOPLE whereas one bar represent TWO-PERSONS and the absence of bar represent PERSON.
This digit is one of a few digits that are "shortened" that don't reflect the ASL sign. Probably for this reason, this digit is also used as an agent (postfix) such as AUTHOR (WRITE+PERSON), DEAF+PEOPLE), etc.
Variation written by ASLwrite, 2014(?).