not sure I would want some heavy handed copper attacking my bike with a hammer and punch though.
I am a retired cop and once did a months attachment to our "Community Involvement" branch, whose job it was to carry out the stamping. As the "boy" of the department, it was my task to go and greet any member of the public who brought their bike in to have their postcode stamped onto the underside of the BB. I used to cringe with embarassment when some poor kid brought their new pride and joy to me, then have it attacked with a hammer and punch. Flakes of paint chipping off for about a centimetre radius around the stamp. At least I used to recommend that they put a coat of clear lacquer over it when they got home (our service didn't extend to such luxuries!).
This was well before the days of carbon frames, I am pleased to say. I don't suppose the owners of some of the more expensive Roubaixs etc. would have let me near them with a hammer and punch

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As for the stickers, yes I remember them but no; I didn't keep a stash! No doubt however there will be long forgotten boxes of them in unused cupboards in Police stations up and down the country. Good luck trying to convince someone to go searching for them though

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Edit.... As an alternative, what about "alphadot" paint as used on motorcycles? A bit expensive at £25 for the kit but it can be used to mark each part of your bike, and comes with "hard to remove" warning stickers.
http://www.alpha-dot.co.uk/index.html