A while ago, somebody mentioned a Masi engraved with the SSN of the previous owner.
Here is what I found in Bicycling 11/1973, p. 46:
"Engraved-ID drive to curb bike thieves
[...] The bike owner's (or his parent's [sic!]) Social Security Number iwll be engraveed deeply into the bicycle frame, and alist of all engraved bikes will be sent to every police district in the city (Chicago)[...]
The biyccle frame is engraved one-sixteenth of an inch deep, making removal without defacing the bike nearly impossible."
There you have it. Good thing not too many owner of truly nice bikes participated!
Jan Heine, Seattle