Thanks, guys, for chiming in. Yo've pretty well covered it, I think.. although I have bought good P38s loose in a box. You just sort of learn to recognize the real thing. I ususally look in surplus stores or on eBay, not in camping stores.
Above all, don't buy anything in a bubble pack. Study the ones that come in bubble packs to see what the fakes look like. And, of course, never buy anything in a bubble pack backed in green cardboard with a red stripe in the corner. <img src="/images/graemlins/wink.gif" alt="" />
My favorite ones are stamped SPEAKER (some that I've had for decades are black from oxidation- still work fine), but there were a lot of contractors. There have been previous threads on these things.
Mostly, they're so tiny, lightweight and cheap that it's just silly not to have one on your person or in a kit, and in that respect they're a great companion for the (also amazingly small and inexpensive, but effective) BSA Hotspark. I only wish more pieces of equipment had those qualities.