He took to Instagram to show the marking on his most prized instrument — a 1957 Martin D-18 guitar worth thousands of dollars.
"The problem is, it's a vintage guitar [from] 1957 and the outside of old instrument is fragile," he told NBC News via his official Facebook account.
The instruments "were all marked — even my harmonicas! So silly," Adams added.
A source at the airport told NBC News that the incident was "nothing new, the system is the same."
The official, who spoke on condition of anonymity because he was not authorized to speak to the media, said: "We mark it to be sure the same item that came in the country left the country."
This wasn't the first time Adams' instruments have been tagged by airport officials. He took to Twitter in July 2015 to allege that one of his guitars had been written on by Air Canada staff.
Adams is currently on a world tour to promote "Get Up," his 13th studio album released in October last year.
He was keen to stress that the incident had "not dampened my love for Egypt — I love the country and its people" but said that was "just extremely unfortunate that the customs people at the airport had no respect for our musical instruments."