What does "sign in" mean?

To sign one's name on a list when entering a place, to indicate one's arrival.

What is a synonym for "sign in"?

Common synonyms include: accomplish, achieve, approach, arrive, arrive at, attain.

verb

verb ·Uncommon ·Advanced level

Verb

1
To sign one's name on a list when entering a place, to indicate one's arrival. idiomatic
"In order to get into the office after hours, you'll have to sign in at the security desk."
2
announce one's arrival, e.g. at hotels or airports wordnet
3
To take some action to access a secured program or web page on a computer; to log in.
"He signed in using his own cybername: Point Guard."

"In order to get into the office after hours, you'll have to sign in at the security desk."