From Longman Dictionary of Contemporary Englishsign up phrasal verb1 SEto put your name on a list for something because you want to take part in it for I’m thinking of signing up for a yoga course.sign up to do something Over half the people who signed up to do engineering were women.2 WORK FOR somebody sign somebody ↔ up if someone is signed up by an organization, they sign a contract in which they agree to work for that organization Several well-known researchers have been signed up for the project. → sign→ See Verb table
Examples from the Corpus
sign up• Allegre was signed by the New York Jets.• Six episodes of the show have been taped, and the actors have been signed for six more.• The band have just completed a highly successful US tour, and several record companies have offered to sign them up.• England soccer star Paul Gascoigne was signed up by a top Italian club.• Gary can't find a job, so he's signed up for Unemployment Training.• I signed up to take an art class just to get out of the house in the evenings.• Did you sign up yet? The course starts in two weeks, you know.sign up to do something• Unfortunately she had signed up to act in a film two weeks earlier.• As I have already suggested, this interpretation of what Britain signed up to is highly debatable. 