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Douglas Harper's Etymology Dictionary

1968, from the verbal phrase; see sign (v.) + in (adv.).

Usage examples of "sign-in".

And when he was printing his name on the sign-in sheet it matched the print of the joke on the gift card.

I put in a good word for you, but when the honchos came here from Dix and looked at all the blanks in the sign-in book, the shit hit the fan.

There was a sign-in book and a silver bowl containing jelly beans on the table.