Adams, who was in Cairo for a concert at the Giza Pyramids on March 8, posted a picture of the vintage Martin acoustic guitar on his Instagram account.
A number and an illegible word in Arabic had been scrawled in green ink on the guitar's mahogany side.
"Airport customs graffiti on my 1957 Martin D-18 from Egypt. Back to the luthier #bryanadamsgetup," Adam's wrote on Instagram, referring to his latest album Get Up!.
Adams, best known for his hits "18 Till I Die," "(Everything I Do) I Do it For You," and "Please Forgive Me", said his problems with customs had begun on his arrival at Cairo airport.
"We almost didn't get the equipment into the country, and when we did it was all marked like this," he told AFP in a Facebook message on Friday.
"There were absolutely no apologies."
A customs official at the airport told AFP that instruments are marked with serial numbers, although usually with stickers.
Regarding the ink, he suggested: "Maybe it wasn't us?", although the script was Arabic.
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Egyptian wits took to Twitter to mock the incident.
"Doesn't Adams know that we glued together Tutankhamun with super glue? It's normal that we write something on a 60 year old guitar," one wrote, referring to a botched repair of the priceless Tutankhamun funerary mask in Cairo's museum.
The Oscar-nominated musician said he would still return to Egypt to perform.
"I have no grudges," he told AFP.
"Rest assured, apart from this incident, I love Egypt and look forward to returning again one day."
"But without the green paint markers please."
It is not the first time that someone has scrawled numbers on one of Adams' guitars.
In 2015, he complained on Twitter that Air Canada had taken a marker to his guitar, scrawling a serial number in black ink.