Parking can be difficult. We suggest you take the the train. The Blue Line Damen stop lets you off practically right across the street from the shop, so if you have that option, that is ideal.
If you must drive, allow yourself extra time for parking; especially on the weekends. The City of Chicago has a handy Parking App called ParkChicago that allows you pay for your parking meter & add time to the meter via an App, we suggest downloading this App and having it ready to use before your appointment. Most of the parking around the shop is meter parking so this will come in handy & save you a trip down the block with a half finished tattoo.