sign up

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• verb transitive To add a name to the list of people who are participating in something.
• verb intransitive To add one's own name to the list of people who are participating in something.
• verb intransitive To agree to purchase some good or service.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• verb engage by written agreement
• verb join a club, an activity, etc. with the intention to join or participate,