Security tags deter would-be bike thieves and help the police recover your bike if it stolen.
There are various places you can get a security ID tag, however I recommend:
The tags you can purchase from both are highly tamper resistant. The security tags may look like simple stickers, but they are very hard to remove.
Order your chosen ID tags and carefully attach them on a clean part of your frame in the locations recommended by the instructions.
Then, register your bike with the ID tag number and frame number along with a picture on either Bike Shepherd or Bike Register.
Bike Shepherd also offers a mobile app that allows you to scan codes. This is useful if you are purchasing a bike and you wanted to check if it was stolen.