CHICAGO (CBS) — Police have issued an alert in the Fuller Park and Bronzeville neighborhoods, after two recent armed robberies.

In each case, a man entered a fast food restaurant in the evening, and placed a note on the counter announcing a robbery. He then took money from the cash register and ran away.

The first robbery happened around 10 p.m. on May 13 near 54th and Wentworth, just off the Dan Ryan Expressway.

The most recent heist happened around 8 p.m. Sunday near 47th and Champlain.

Investigators said in one incident a witness saw the handle of a gun.

Police have provided only a vague description of the suspect.

Investigators recommended business owners install surveillance cameras and hold-up alarms near the cash register, and train employees on how to safely deal with robberies.

Anyone with information on either robbery should call Area Central detectives at 312-747-8384.