Police forces across Europe hold recovered bicycles they cannot return. Not because they do not know whose they are in principle, but because nobody can prove it.
Finland's police put the problem in a single sentence, with the exclamation mark their own:
"Sarjanumeron avulla poliisi voi etsintäkuuluttaa pyörän. Ilman numeroa voi olla mahdotonta yhdistää löytynyttä pyörää ja omistajaa!"
"With the serial number the police can circulate the bike as wanted. Without the number it may be impossible to connect a recovered bike with its owner." Poliisi
Germany's cyclists' federation, the ADFC, describes the same failure from the other end: many recovered bikes do not get back to their owners despite having a frame number, because the owners cannot describe their bike unambiguously and never wrote the number down.
What happens to the rest is not a mystery either. As Kriminaloberkommissar Ulrich Golla of the Bonn police has described it, unassigned bikes stay with the police and the prosecutor decides their fate, and in big cities there are repeated auctions of bicycles that could not be matched to an owner.
The fix takes about five minutes and you only do it once.
What police actually ask for
This is not guesswork. Several European forces publish the list.
Sweden's police are the most specific, asking for the frame number, the type of bike, its make and colour, whether it was locked, and any distinguishing marks. They also publish a printable owner's card, Min cykel, with a page for photographs. Their instruction is blunt: note the frame number, and "then the chance increases that we can identify it and give it back to you."
Germany's police prevention service recommends a Fahrradpass recording frame number, make and type, kept together with a photo and the purchase receipt, ideally digitally. Austria's Bundeskriminalamt says the same and adds that with that number "a search can be started."
The Dutch police list is the most human: make and colour, scratches, the type of lock, the sticker from the bike shop, and the frame number, which they describe as a unique number engraved on the underside of the frame.
Notice what recurs. Not the brand. The number, a photograph, and the receipt.
One important difference between countries
There is a genuine split worth knowing, because the internet will tell you the wrong one.
In Austria, the official Fahrradpass is treated as proof of ownership. In Germany, the police leaflet says the opposite in as many words: the Fahrradpass is not sufficient as proof of ownership, and for that you need the purchase receipt.
So the receipt is not optional paperwork. In Germany it is the thing that proves the bike is yours, and in every country it is what an insurer will ask for.
In Latvia, the police point at the state register: in the event of a theft, police will search for the lawful owner by the bicycle's frame number. In Denmark, the frame number is effectively a precondition for claiming on insurance at all, and Danish frame numbers even follow a fixed format, one to five letters, then at least one digit, ending in a letter.
Elsewhere there is no format at all, which is the next problem.
Frame numbers are not standardised, and that is the point
People assume a frame number is like a car's VIN. It is not. The ADFC states it plainly: manufacturers stamp frame numbers with no discernible system, with duplicates, and with no central customer registry.
German police add an operational warning: some bikes, especially from mail-order and department stores, carry order or article numbers that are not individually assigned and are therefore useless for a search.
We could find no international standard for bicycle identification numbers. ISO 4210, the standard people reach for, is a safety and test-method family, not an identification scheme.
The practical consequence: your frame number is only useful if you recorded it, because nobody else did. And where it is stamped varies. Police sources name the underside of the bottom bracket most often, then the seat tube and the head tube. The German police form offers just two tick-boxes, bottom bracket or seat tube, which tells you how predictable it usually is. Our guide to where to find your bike serial number covers the rest.
What a complete record contains
The German and Austrian police forms are the best template available, because they are forms police designed for their own use rather than a vendor's wish list. Between them they ask for:
Frame number, and where on the frame it is
Make, model, frame material and colour
Purchase date, price and dealer, with the receipt itself kept
Photographs of the whole bike, saved somewhere other than the bike
Distinguishing features: damage, stickers, non-standard parts
Components: gears, brakes, lighting, tyre size, suspension
For an e-bike, the battery serial number and the motor and battery positions
That last one is easy to miss and both forces ask for it specifically.
The components matter more than they look. A thief changes a saddle and sprays a frame. They rarely change the groupset, and "Shimano 105, 11-speed, with a cracked left shifter hood" is a description that survives a repaint.
Almost nobody does this
Austria's road safety board surveyed 1,520 people in June 2026. Among e-bike owners, who are the best-prepared group of all, only 37% had noted the frame number, 47% had kept the purchase receipt, and 23% had registered the bike.
Those are the careful ones. Owners of ordinary bicycles do worse.
The same survey found nearly one household in four had a bike, e-bike or e-scooter stolen in the previous five years, and that a third of victims did not report it to police at all. A theft that is never reported cannot be matched to a recovered bike by anyone.
Documentation does not stop a theft. It decides what is possible afterwards. A peer-reviewed study of 1,823 thefts found that among bikes that were recovered, registered owners more often got them back through the police, 38% against 32%, while unregistered owners relied more on online channels. Registration does not make a bike reappear. It gives police something to match against, which is the route that works once the bike has left your reach.
Do it now, while the bike is in front of you
Autumn is the right moment, because the bike is about to go into a shed or cellar for months and you will not look at it closely again until spring.
Find the frame number and photograph it, rather than transcribing it. A photo cannot drop a character, and 0 against O is a real problem on a stamped frame.
Photograph the whole bike from both sides, plus any damage or stickers.
Find the receipt and save it with the photos. If you bought privately, keep the message thread and the seller's details.
Note the components, and the battery serial if it is an e-bike.
Store it somewhere that is not the bike and not only your phone.
Then it is done, and the next time it matters you will be filling in a police report from a record instead of trying to remember what colour the bike was.
Five minutes, free: register your bike and keep the frame number, photos and ownership record in one place. Before it goes into storage, the winter storage checklist covers the rest.
