Opportunistic thieves are now frequently targeting contactless credit and debit cards, which can be used without a pin number, police say.
They are looking for a thief who stole workers' handbags from a Hamilton store, then used the cards in them at various places around the city, particularly service stations.
Sergeant Neil Fenwick said people should be aware of how vulnerable the cards were to theft and keep them stored out of sight.
Retailers had the right to ask people using the cards for identification, and should do so if something doesn't feel right, he said.