This sign is part of indexing in ASL. You need to describe who you are talking about before using an index sign.

Plural forms of THEM

TWO-OF-THEM

THREE-OF-THEM

You can learn more about pronouns and indexing in ASL 1 - Unit 7 and in Chapter 6 of Don't Just "Sign"... Communicate! A Student's Guide to Mastering ASL Grammar.