CHICAGO (WLS) -- A 55-year-old grandmother was mugged early Monday morning while waiting at a CTA bus stop on Chicago's North Side.The woman was waiting for the bus in the 2400-block of North Ashland Avenue around 4:50 a.m. when police said woman driving a red SUV pulled up and two males got out of the vehicle and pulled out handguns. Police said they took her purse and fled the scene.The grandmother suffered a bump to her head and was transported to Illinois Masonic Medical Center for treatment, police said.No one is in custody.