A valid entry visa.
A green and a red stamp in the short film adaptation.
Stamps are inked impressions the inspector adds to an entrant's documents, usually a passport, to show whether they are approved or denied entry into Arstotzka. In addition to passports, passport seizure slips, temporary visa slips, and Jorji Costava's fake passport can also be stamped.
Initially, there are only entry approval and entry denial stamps. From day 18, reason for denial stamps must accompany all denials. In the booth, entry and denial stamps are attached to a bar that slides above the table when clicking on a bar in the right-hand side of the screen (in the desktop version). It is possible to install an upgrade to make tab and enter keys reveal the bar to speed up processing. The reason for denial stamp appears automatically when a discrepancy is detected.