I have no papers for the bike I bought brand new at full retail from a bike shop. Who keeps "papers" for a bike?

They probably just mean proof of purchase. The other important bit is the serial number (analogous to a car's VIN), often found under the bottom bracket.[0] You can (and should) register it with the local police, and there are a few online registries too. It's not an effective deterrent[1], but it's better than nothing. (I've had a bike returned to me because I registered it. That was before I learned to always use Kryptonite U-locks.)

[0] https://bikeindex.org/serials

[1] Wrapping your bike in tape, or otherwise making it look like a POS, is the way to go if you live in a theft-heavy location.

Yeah, I didn't keep any paperwork or proof of purchase unless it's in a random box of junk somewhere. It didn't even occur to me to do so. I probably kept the sales papers for a little while in case I needed it for a warranty claim, but if I have them now, I don't know where.

> always use Kryptonite U-locks

Don't. My bike was stolen by rapidly sawing (dremeling?) through a Kryptolok in broad daylight in a place with some of the most heavy law enforcement presence in Europe. Their locks are much weaker than their marketing.

Kryptonite are plenty strong, they are a good deterent, but not theft proof by any means. I've talked with people who's job was to cut bike locks. It was generally something like cables, 15 seconds. Offbrand u-locks 45 seconds and 1/3rd of a cutting wheel, name brands minute in a half and a cutting wheel. Then the "new york style" heavy ulocks were on the order of 5 minutes and 3 wheels.

Certainly there are bigger cutting discs, if you are willing to make a bunch of noise and sparks you can cut them more quickly.

Sorry to hear that. It's the strongest lock I've come across[0], but yea, once power tools come into play I can't imagine much of anything standing up to metal cut off grinder. What do you use now to secure your ride?

[0] http://www.kryptonitelock.com/content/kryt-us/en/products/pr...

What locks are stronger?

Well, not you? The receipt typically has the frame number and it's your proof of ownership.

You should keep it just so you can get your money back from insurance if it is stolen..

I never even registered my bike for insurance. It didn't occur to me and I'm not sure it really crosses the threshold of value/hassle for me.

The bigger point is that it's unreasonable to paint all people who buy used bikes without papers as supporting bike thieves. Anyone buying my bike would not get paperwork with the sale, but the bike is not stolen.

> The bigger point is that it's unreasonable to paint all people who buy used bikes without papers as supporting bike thieves.

It's absolutely accurate to portray them that way; sure, there are some used, no-papers bikes that are not stolen, but people willing to buy such bikes are what creates financial support for bike thieves, since all stolen bikes sold meet that description, and if people weren't willing to buy bikes in that condition stolen bikes couldn't be sold.

I've had a bike stolen where the frame manufacturer offers a simple online service to report a bike as stolen. There is zero excuse for anyone buying it to not check the number that is engraved onto the frame, not to mention with police who similarly have the serial number in a database.

Imagine if people had to drive around in creaking beater cars with leaking roofs because you couldn't store anything nicer anywhere but a garage with surveillance, and even then if someone finds out you have a nice car in a garage, there will be a breakin. That's pretty much the situation with bikes, and police simply shrug at what in most cities is very much organized crime and a huge quality of life issue.

> but people willing to buy such bikes are what creates financial support for bike thieves, since all stolen bikes sold meet that description

All stolen bikes also have two wheels. I guess buying a bike with two wheels also creates a market for stolen bikes?

This is ridiculous. No one without papers can sell a bike according to you. I get that bike theft is a problem but you don't solve it by blaming innocent people. A lot of legitimate bikes are sold without papers.