I think that for bikes that don't have serial numbers, your insurance company will likely accept your original papers as proof of ownership. I've heard it helps to have pictures, too, although my company didn't ask for pictures. In my case the serial number was critical, since my only other documentation was my bank's record of the EFT when I bought the bike from its original owner. Without a store receipt, my claim would have seemed sketchy from the insurance company's perspective. The serial number proved to the insurance company that the bike existed in the first place, that it was of the make, quality and size that I said it was. If your bike doesn't have a serial number but you have a bill of sale and paperwork describing the bike, you're probably okay if you need to prove to your insurance company that you had a bike that you no longer have.

For the purposes of identifying a bike as yours, if it's recovered? That's a different question . . . serial numbers can be scratched off, so they're not foolproof. I think having pictures & detailed description helps a lot, especially if your bike is custom or unusual somehow. Even if it's been altered. I keep thinking maybe I'll see my old frame out there that's somehow been built up differently than it was when I last saw it. I would love to have that frame back.

I've been reading a lot of threads on other boards about different strategies people use. Some people will put some ID, like a business card inside the handlebars, or inside the tire, hoping that if an honest person unknowingly buys their stolen bike and finds it that maybe they'll return it. I saw that one guy had his framebuilder engrave his SS# inside the bottom bracket, where only he will know to look for it, and a thief hopefully won't think to go in there to scratch it off.

I'm also looking at different bike racks built for inside storage, something that I can bolt to my foundation or to studs and be able to lock my bikes to, so that even if someone gains access to my garage again it won't be so easy for them to take my stuff.