Hmm well it is cheap and lo tech idea and certainly not full proof but i would maybe get some sort of covering (BMX thingies, hose) To pull over the Couplers when parking the bike. It won't fool close inspection but the opportunist thief will likely not see the Bling/shiny couplers when he walks by and hence will hopefully not get ideas.

But at the end of the day i feel S & S couplers are almost never worth the outlay or better than a good folder. The exceptions would be if you are a pro racing cyclist, you have real reasons for wanting full size geometry (despite the advantages of smaller wheels/frames) etc.

Remember you can get a whole lot of complete folding bike for the money just a decent frame and S & S couplers & retrofit go for!! Since folders have become so good and are have been convincingly used for anything from Traithlon, to setting speed records to the longest most gruelling tours the choice seems obvious...