The incidents happened on July 1 in the 3100-block of West 26th Street and on July 7 in the 2600-block of South Spaulding.
Police say the man showed a badge, stopped the victims and searched them.
"He's stopped individuals in their cars and he's asked for identification. At this time, the victims would produce a wallet and what he would do is take money out of the wallet, give back the wallet and then leave," said Chicago Police Commander Berscott Ruiz.
Police say the offender may be driving green Mazda.
Officers say if you think you're being stopped by someone who isn't police, call 911, or ask the person to call for a uniformed supervisor to the scene.