Fraudsters are using counterfeit £20 notes in scam deals in parts of the city.
The news comes after the Evening Times revealed 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.
However, police said officers are "committed" to ensuring the safety of spectators and visitors.
Officers 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 within 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 mobile phones and computers with counterfeit Clydesdale Bank £20 notes.
Genuine Scottish bank notes have a watermark that is hardly visible until it is held up to light.
A metallic thread is embedded in the paper of all bank notes and 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 under ultraviolet light.
Real bank notes are printed on special paper, which feels slightly rough - not smooth, shiny, limp, oily or waxy.