It is also worthwhile every time you do a mod to the bike- add a new part etc, take a digital photo of it, the bike as let's face it, digital photography is free and cameras have come on leaps and bounds, so high res images are totally possible.
Also all my components are marked with a series of light dot punch marks in the form of a star constellation, to outward observer they look like if they look closely just wear and tear, but apply a stencil I have made and a constellation is revealed, a positive ident mark that doesn't look like an ident mark.
Also well down the seat tube and fork there is a sealed plastic bag containing the note; This ........ was stolen from........
The Saracen I had stolen never turned up and neither did the parts end up on ebay as I was watching for about six months and those parts were star marked too. But I hope the thieving scrote had fun getting the snake eye security cap screws undone if the bike was stripped and didn't end up chucked in the sea. But that bike was well marked in lots of different places.
Also another my GT has had and that is the Berol security pen written all over the frame, invisible in daylight, but a fuzz with a UV lamp can read all.
Me though I take my bike security seriously, if it does get stolen I wish my bikes to be a pain in the ass and incriminating to thieves if and when they are caught as it is habitual criminals cops do check other stuff they have in case that's stolen too and of course I wish for bike thieves to feel the full weight of the law so I mark all my stuff.