Advertising trailers parked in public parking – is that allowed?

Moin. With me in the street someone has just put an advertising trailer (“Wäschecenter” in a parking lot. Now here, as everywhere around the Hamburg Alster, there is a quite lack of parking spaces. The parking lot, in which the trailer was parked, is large enough for an above average large vehicle. The trailer occupies about half(!!) of the area. The parking lot is limited by a street lamp in front and a tree in the back. Just like the trailer now s I’m just annoyed that someone in the area (where no one needs a “washing centre”) with such a crap occupies a (half) parking space and thus makes it unusable. May this thing stop there (well, someone knows how long), or do I have a legal way to get rid of it?