Every apt complex I've lived at has had the rule that parking is for residents only, AND guests of residents. If someone is visiting Joe on the 3rd floor from Florida, he gets to park in the parking lot, not elsewhere.
Suppose this guys girlfriend lives in your building, and he visits her on the weekends. You can't get pissed over him parking there. I've been in similar circumstances, and you just have to suck it up. Unless for some whacked out reason your super says that residents and only residents can park there, no matter the circumstance, but that makes it a bitch for when you have friends come over.
Plus, some people lose their stickers/ dont want to stick them on the car. How do you know for sure this guy isnt a valid apartment dweller
Either way, at most tow it, don't fvck up his ride because your childish and overreacting.