sign up

verb

1. To add a name to the list of people who are participating in something.

   “We signed Bob up for kitchen cleanup duty.”

2. To add one's own name to the list of people who are participating in something (including amateur, but not professional, teams).

   “Coordinate term: sign in”

   “Terry signed up for the soccer team.”

3. To agree to purchase some good or service.

   “After much deliberation we decided to sign up for satellite TV.”

4. To enlist in the armed forces.

   “Didn't you hear? He's just signed up!”