From Longman Dictionary of Contemporary Englishsign in phrasal verb1 SIGN YOUR NAMEto 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 ↔ inDLSIGN YOUR NAME to write someone else’s name in a book so that they are allowed to enter a club, an office etc → sign→ See Verb table