How is “sign in” used?

In Never Rarely Sometimes Always (2020), one line is: “Uh, why don't you sign in, take off your coat, and have a seat.”

Which movie is “sign in” from?

The clip at the top of this page is from Never Rarely Sometimes Always (2020).

to write your / sb's name when you arrive at or leave an office, a club, etc.

Oxford86% of films
to write your / sb's name when you arrive at or leave an office, a club, etc.
Uh, why don't you sign in, take off your coat, and have a seat.

Definitions from the Oxford Advanced Learner's Dictionary, 9th edition

Uh, why don't you sign in, take off your coat, and have a seat.

Said in 8 films · #1