Question about a strange vehicle

I saw a vehicle yesterday that made me curious. It looked like a regular, rather large dark blue SUV, but what made me notice it was that I’d heard a siren and looked around, and this vehicle suddenly turned on red and blue flashers not on the roof but kind of hidden behind the front grille. This was on Liège, not a major street, although not far from Crémazie. It zipped past the other traffic and was gone before I saw anything else.

Do our cops have stealth vehicles of this kind? I realize I assumed it was illegal for non-cop vehicles to have sirens and red-blue flashers, but I don’t know the letter of the law.