If you see an X or O, don't panic.
Travelers entering the United States from abroad may notice big black X or O printed on their receipt from the automated passport control kiosk (or APC). No, it is not someone's first Tic-Tac-Toe move.
According to U.S. Customs and Border Protection, there are a number of reasons travelers may receive either of these markings on their receipt. The letters might be flagging for fingerprint recognition issues, duties that need to be paid, additional document checks, random inspections, or questions about their customs declarations forms. (Ask yourself: Did you check "yes" to hanging out with livestock during your vacation?)
“International travelers using the Automated Passport Control kiosks should not be alarmed if a symbol appears on their receipt,” Stephanie Malin, a public affairs officer for U.S. Customs and Border Protection, told Travel + Leisure.
Not unlike seeing an SSSS printed on your boarding pass, these codes on your APC receipt can often (though not always) indicate you're going to experience a lengthier or more involved process for entering the country, regardless of whether you’re a Global Entry-approved U.S. citizen, green card holder, or foreign tourist.
“There are [also] referral codes that appear on each receipt,” Malin noted, adding that those are for “internal agency use only, and allow CBP officers to easily identify where the traveler should be routed based on the referral.”