From today, anyone in Belgium can register a bicycle in the national MyBike database. It’s a government initiative to help in the fight against bicycle theft and is being launched on occasion of the first National Week of Action against Bicycle Theft. Thanks to a sticker with a personal QR code that you stick on your bicycle, the police can find out more quickly whether a bicycle is stolen or not. In Brussels, the system has existed for several years, but now it is also being rolled out in Flanders and Wallonia.
From https://mybike.belgium.be/:
So I’m guessing the best protection is parking your bike with a sticker next to bikes without one.