A series of incidents over the past week have prompted people to report concerns to police or their bank after becoming suspicious while using ATMs.
The scam involves putting a loop of plastic into the card slot, which then traps any card put in the machine.
Customers then believe their card has been retained by the machine and when they walk away the thief removes the device and steals the card.
Another scam being used is card skimming, which involves a device, hidden on the machine, reading the details on the bank card.
This is often in place alongside a secret camera that records the customer entering their personal identification number (PIN).
Scammers can then create a fake or 'cloned' card with your details on it and is able to run up charges on a person's account.
Police on patrol in the city centre are checking cash machines, while bank and building society staff are carrying out regular checks of their own ATMS.
Shoppers are being advised to take extreme care when using cash machines.
Chief Inspector Martin Cloherty, city centre area commander and who is leading the investigation, said: "People should take a little more care when they are using cash machines.
"They should take time to look around to see if there is anything strange or different about the machine.
"If that is the case we are asking that they report it immediately to the bank or the police.
"When people are using their card they should shield their PIN when they are using the key pad. Then, if there is a recording device attached, they are covering their number."
Anyone concerned about a possible cash machine scam should call police on 0141 532 2000.