Detective Inspector Louise Ludwig said: "We would urge all shoppers to be wary of anyone who might be watching you at the checkout.
"Always cover your PIN when you enter it into a cash machine or Chip & PIN machine at the tills.
"Try to avoid being distracted by people asking for directions, and keep your valuables safe."
More top news
Thames Valley Police have spoken out after two men were found guilty of Kerry Reeves' murder
Friday night's forecast for the west of the region
It's a Bank Holiday weekend, with half term for many. Here's how it's looking on the roads, in the skies, and at getaway hotspots