Originally Posted by 77Univega
-- Yes, your concern is well taken but one of the attractions of a folding bicycle is that it can be taken indoors AWAY from the thieves.
an s&s bike can't be easily disassembled and taken inside. Takes quite a while to take apart and you have a bunch of loose pieces to wrangle.
there is no such thing as 100% security as others have mentioned. and as noted above, there is no really good way to lock up the front half of the bike. remove the stem and it's bye-bye front end.
Remember, though, it takes a special spanner to loosen the couplings - a tool few thieves are likely to have handy. If the couplers are properly tightened (i.e. really, really tight) they can't really jimmy it off. anyway, few people are likely to have any clue whatsoever that your bike "unscrews" - they just look like funny lugs to the unknowing.
I had an s&s coupled bike that I would lock up outside to the same extent I would do with any other comparably priced bike.