An upsurge in thefts from cars parked at and near the Costco warehouse store in Northeast Washington has been reported, and police said they are joining with store security personnel to crack down.

Police said seven such thefts were reported last month, three more than in July, the month with the second-highest number. Apparently no more than two were reported in any other month.

“Beware when you park your car at Costco,” said a posting on a police department List Serve. “My window was broken and the radio was removed Friday.” The thieves apparently worked quickly; the victim described being in the store for only 30 minutes.

On the same site, a lieutenant from the 5th District said police were on top of the issue and working with members of the company’s security team.

She also reiterated advice given routinely to people who park their cars in public places: “Remember not to leave anything valuable” in sight.

Another police official called for motorists to stow items out of sight before leaving their vehicles, and specifically not to leave GPS equipment in unattended cars.