sign_up
1. [ verb ] (work) engage by written agreement
Synonyms: contract sign sign_on fee
Examples:

"They signed two new pitchers for the next season"

Related terms: hire contract_out contract
2. [ verb ] join a club, an activity, etc. with the intention to join or participate, "Sign up for yoga classes"
Related terms: join enlist
Similar spelling:   signpost
  sign_off
  sign_over