I work at the airport of Charleroi, but that doesn't give me any advantages, apparently. I was parking where I couldn't park (ok, my fault), and instead of a fine, the airport police put a sticker on my car window, so I could hardly see anything anymore. I couldn't get it off and had to drive home like this. Not very safe, is it ? And imagine the faces of people on the highway, seeing me with this thing on my window! ;-)))
So, a good advice: park where you are allowed to!
If you have to be at the airport, then please park at the airport parking spots. Parking on the side of the road or in the industrial zone opposite the airport is at your own risk. We get a lot of passengers whose car have been damaged this way!
OKAY...Charleroi is renowned throughout Belgium as the most violent and dangerous of its cities, and it does live up to it. Generally the atmosphere is cool, and has a rough charm that you come to recognise, but the streets tend not to be lit at night sometimes and there are plenty of people lurking about. However, in June 2000 Charleroi of all places is where the infamous fans of England and Germany converged for the Euro 2000 football match, and the police were ready with water cannons - it was the English who caused the problems though, taking offence at others for celebrating their own victory (ie the French on the freiday) and throwing chairs. The Germans were not interested in joining in a stupid riot (rather like out in the Gulf..) and the English thugs made prats of themselves, and totally embarassed me - although I was ok, I was hanging out with my very large African neighbours!
Regarding crime, Charleroi is often called the "Chicago of Belgium". Maybe it's a bit exaggerated, it's very unlikely that you'll get killed during your stay! ;-)
The major problem is car jacking and damaged cars. During daytime you'll be ok, but at evening or nighttime, please park your car on a safe spot. Dark alleys aren't really an option here. Robbery can be another hassle. Once again, during daytime, no problem at all!
Hope this doesn't scare you off too much. Anyway, I regularly go to Charleroi and never had any problem at all!