sign up

sign up  {v.}

1. To promise to do something by signing your name; join; sign an agreement.

We will not have the picnic unless more people sign up.

John wants to sign up for the contest.

Miss Carter has signed up to be the chaperone at the dance.

2. To write the name of (a person or thing) to be in an activity; also, to persuade (someone) to do something.

Betty decided to sign up her dog for obedience training.