My bike is registered with, https://www.bikeregister.com. It won't stop a theft but might act as a deterrent. Also, you might get it back......
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My local community used to require bike licensing, license lasted three years and helped generate fee revenue. Vast majority of people did not register their bikes but I always registered each bike once, but I did not renew them. If it was stolen and police recovered it, the number on the sticker correlated to my contact info in the database run by the city. Decades ago my dad got his bike back that way after it was stolen.
I got an e-mail last month, pasted the text from some of it below:
This letter is to inform you that on January 5, 2021, the Madison Common Council voted to repeal the City of Madison's mandatory bicycle registration requirement. As of that date, Madison residents are no longer required to register their bicycle(s) with the City. Effective immediately, the City will no longer be accepting new bicycle registrations or renewals. The existing bicycle registration database will be active until the last current registrations expire on May 15, 2024. After that, the database will still be available for searching any previous registrations for the foreseeable future.
The City still believes that there is value in registering bicycles, but our registration program was very limited in its reach. Registering your bicycle with a national bicycle registration database greatly increases the chances of recovering your bicycle if it goes missing. There are two national Bicycle Registration programs, Bike Index and Project 529. Registering your bicycle with either of these programs will store your bicycle's important information into a nationally accessible database. Registering your bicycle with either program is free. If you would like to have a registration decal for your bicycle, you may purchase one from either program after you register with them.
Even though either program will protect your bike, the City of Madison has decided to partner with Bike Index at this time.Based on that, I recently registered all my bikes with Bike Index. And I will put a sticker on each bike that lists the bike as registered with Bike Index, I should get the stickers in the mail any day now.
That said, there might be some regional bias where some registration systems are preferred over others in certain regions, so maybe Bike Index won't be the go to solution in the UK?
A guy I know a few years ago said that his daughter's bike was stolen, but when she found it for sale later on-line, the police would not help her get her bike back because she had no proof of ownership. A registration program is not proof of ownership, but it could still help with the police in a situation like that.