On wikipedia it explains that there are ALTERNATE SIDE laws, which really just means that it is illegal to park on a certain side of the street (due to street cleaning, sweeping, snow plows, etc.) This is a very common infraction which is just a fineable offense.
George gets a job moving everyone's cars to avoid the fines, but he really sucks at it.
Watch the episode for more info...
http://en.wikipedia.org/wiki/The_Alternate_Side