Fraudsters are using counterfeit £20 notes in scam deals in parts of the city.
Police had warned that criminals planned to flood the city with thousands of fake bank notes during Commonwealth Games.
Experts fear retailers will be the main target, during the sporting event, for fraudsters using counterfeit cash.
Police are urging both locals and visitors to be vigilant when they handle currency, after reports of fake £20 notes circulating in Maryhill.
A police statement warned: "Counterfeit currency is in circulation in the Maryhill area, specifically £20 notes.
"Check all money and report anything suspicious."
Shop staff and sales desks are expected to be under "increased pressure" during the Games, making it more likely for fake notes to be accepted.
Fake cash leaves shops with the worthless currency and out of pocket after having given real cash back as change, as well as losing the items the con artists have "bought".
Last year, police launched an investigation after conmen targeted Glasgow shops with fake bank notes.
The fraudsters bought high value items, including mobile phones and computers, with counterfeit Clydesdale Bank £20 notes.
Genuine Scottish bank notes have a watermark and a metallic thread is embedded in the paper, which appears as silver dashes on the back of the note.
When held up to the light, the metallic thread appears as a continuous dark line.
Each note also has an individual serial number and fluorescent features, which show up only when they are exposed to ultraviolet light.
Real bank notes are printed on special paper, which feels slightly rough - not smooth, shiny, limp, oily or waxy.