sign in phrasal verb (see also sign)

1. to write your name on a form, in a book etc when you enter a place such as a hotel, office, or club:
Remember to sign in at reception.

2. sign somebody ↔ in to write someone else’s name in a book so that they are allowed to enter a club, an office etc

[TahlilGaran] Dictionary of Contemporary English ▲

sign in
to write your name on an official list when entering a place.
Messengers are required to sign in at the front desk.

Usage notes: sometimes used in the form sign someone in - to write someone's name on an official list when they enter a place:
An elegantly dressed young woman signed us in at the door.

Opposite of: sign out

[TahlilGaran] English Idioms Dictionary ▲

sign in
v. To write your name on a special list or in a record book to show that you are present.
Every worker must sign in when coming back to work.
Teachers go to the office and sign in each morning before going to their classrooms. Contrast SIGN OUT.

[TahlilGaran] English Idioms Dictionary ▲