getting people to secure their bikes properly in the first place might be a better place to focus your efforts
Believe me the police do a lot of work on this. Bike theft in Bristol has actually come down by nearly 10% over the past couple of years but I don't think that's the high-end stuff, it's poorly secured bikes that are left unlocked or cable locked.
My bike doesn't have a serial number
Borrow a set of letter punches, hell, even a dot punch and mark it.
The police use a system for filing theft reports which is well out of date and not relevant to modern MTBs (Sample questions: "Does it have more than 7 gears?" "Does it have basket?").
Unless you expect the jobbing officer who investigates to be able to identify, for example, the difference between an SLX and an LX groupset, the serial number is your best bet. Not everyone is a bike nerd but anyone can check a serial number.
If sellers list the number and you don't have it in some pre recorded data it would be useless?
So note down your serial number already! Then you'll be able to give it to the police when you file a theft report. There are lots of unclaimed bikes at police stations and a key reason is people not recording serial numbers.
The thieves just gonna break our bike and will sell it as spare parts which is a hundred times more difficult for us or the police who monitor this thing. ..
They're doing this already, in some cases they'll even cut through a frame to steal the parts. However this writes off the most valuable bit of many bikes, and is a lot more effort.
If we could also do this for suspension forks it would be amazing.