* If you're referring to a specific person, but you don't know who they are: You would use the sign for "person". This is made by touching your chin with your index finger and then moving your hand out and away from you.
* If you're referring to a person in general, without specifying who: You would use the sign for "they". This is made by pointing your index finger outward, then moving your hand forward and slightly downward.
It's important to note that there are other ways to indicate "someone" in ASL depending on the sentence structure and the specific meaning you want to convey.