SANDY SPRINGS, Ga. (AP) — Police in Sandy Springs are warning fast-food delivery drivers to be on alert after a number of robberies.

Police in Sandy Springs, just north of Atlanta, believe four recent robberies are related. They’ve stepped up patrols on the north side of the community in response to the crimes.

Sandy Springs police Capt. Steve Rose says in two of the cases, the suspects called from a specific number but police have not yet been able to trace the source.

Police have posted signs at restaurants telling drivers to beware of calls from the number and to call police if they receive one.