Every Gunnar goes out with a serial number. The number may be hidden under the paint, but every frame gets one. Check out the FAQ section at http://Gunnarbikes.com
to find out where the serial number is and what it looks like.
Paint can, sometimes, obscure part of a serial number. With a model, size and history, we can fill in partial serial numbers. It is very rare that you can't see enough of a serial number to identify the frame.
If the serial number has been removed, I'd be concerned about foul play. You certainly would not want to buy a stolen bike. We have a record of virtually every Gunnar ever built. If you want to buy a used Gunnar, you have the right to validate the serial number.
We're so serial number-obsessed that we require a valid one for every Gunnar registered (new or used). Once you register your Gunnar, you can report it stolen and we'll keep an eye out for it.