Can you not "abuse your position" and make an "official visit" with a couple of colleagues, flash badges and so forth? I realise the stupidity of this type of abuse of power, but if it was done with subtlety, it might work....

Well, I have three problems when it comes to that.
The first one is integrity. I can honestly say that I've never abused my power to get personal gain, and I'd like to keep it that way. Call it a concience thing if you will.
The second reason is that it's out of my jurisdiction. Here in Belgium, the police has no jurisdiction in civil matters (which this clearly is)

However, this DOESN'T mean that I don't know what to do when push comes to shovel. If UPS wants a fight, I'll let them have one. I know my rights and I know which legal institutions I can use and how to use them.

The third reason is that I don't have a clue where to go to to complain in person. UPS is one of those firms that doen't have a real address, and the people you need are never where you expect to find them. E.g. when I phoned to complain about what happened yesterday, somehow I ended up in Holland in their Dutch department. Patching me though to the correct department was not possible of course.

Come to think of it : I have flashed my badge once when I wasn't on duty (which doesn't make much difference because according to the law I'm 24/24 "on duty").
See, I had parked my car on a parking spot near the dorm where my girlfriend lives. I stayed there for the night. When I got back the next morning the number plate of my car was gone. There was a note behind the windshield wipers. It was from the janitor (sp?) The note stated that the space I occupied was a private space and that I had no business being there. It said I could pick my number plate up at his office and that I had to pay a 100 euro fine.

So I went there. And I let him speak. He had that look in his eyes like : "I've got this sucker now and I'm going to give him a piece of my mind"
The conversation went something like this :

Him : "Aren't you ashamed to occupy somebody else's parking space ?"
Me : "I'm sorry, I had no idea this even WAS somebody elses space. How was I supposed to know, there's no indication of this anywhere. But aren't you ashamed to steal somebodys licence plate?"
Him : "I have the right to do so"
Me : "Says who ?"
Him : "The police. I've contacted them and I know who you are, this is your identity" (he showed me a small piece of paper which indeed stated my identity)
Me : "Oh, I see we have a problem here. What do you suppose to do now ?"
Him : "Simple. You pay 100 euro's, you get your licence plate back and you move your car"
Me : "That might be a problem"
Him : "Howso ?" (It was clearly showing that he was feeling pretty good about himself at this point)
Me : "Because you've made the mistake of unscrewing the wrong person's licence plate!"

At that time I flashed my badge. His face turned as white as paper, and this didn't improve when I told him that he had exactly 10 minutes to screw my licence plate back on, or otherwise I'd arrest him for stealing and damaging personal property, embezzeling (sp?) an official document (which a number plate is) and deliberately trying to rip off people (can't remember the official term in English).
I also demanded to know WHO the police officer was that gave him my personal data through my number plate, because this was clearly a breach of that person's professional secrecy. (I don't know if this is the correct term, but you know what I mean).
I fully intend to contact the police force's internal affairs and inform them about this collegues' loose morals when it comes to his profession secrecy. In my book that's one of the biggest mistakes you can ever make when you're an officer of the law.

Anyhow, ten minutes later I drove on, WITH my number plate.

Every time I see this guy now, he's extremely polite. Up to a point where he would probably even wash my car if I asked him to.

It still feels pretty good when I think about it.