sign_up has definitions from the field of work
1
[ verb ] (work) engage by written agreement

Examples

"They signed two new pitchers for the next season"

Used in print

(The Times-Picayune, [New Orleans]...)

The promoter who wanted to sign him up for the circus asked him how he was able to do it .

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"

Used in print

(San Francisco Chronicle...)

Sustaining members may sign_up at $ 25 for the ten-concert season ; annual members may attend for $ 16 .

Related terms

join enlist

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