Stopping the trade in stolen bikes

Andrea from Velorution makes a valid point in a recent post that would make it significantly harder to sell a stolen bike.

He wants online bike ads to be removed if they don’t include the bike’s frame number.

This seems like common sense however do you have your bike’s frame number written down, even if you’re not registered with Immobilise?

If not, how do you expect to get your bike back if is stolen?

Surely you can’t be prepared to just write it off and buy an new one?

Also, would you check the frame number before buying a second hand bike?