Signed-in users can also find this guide, with screenshots, under Help in the app.
Some cars come back again and again. ParkCommand flags them in three places so you can act, for example by blacklisting them.
On Check vehicle, look at History under the result. It lists recent violations for the plate, with a red badge counting the open ones.
During a patrol, a plate that had a violation at this building in the last 90 days shows REPEAT OFFENDER on the result, and repeat in the list of checks.
On Reports, the Repeat offenders card lists every plate with more than one violation in the dates you chose. The Patrol report has the same card for patrol periods.