I had taken for granted that packaged foods marked with just "K" are not necessarily kosher--that is, that "K" is not a real hechsher--because the company prints that symbol itself, and it does not necessarily indicate rabbinical supervision or sanction. (Certain items marked "K" are on kosher lists; these, like other items on relaible lists, are OK.) Or so I thought.
However, I have been seeing some discussion to the effect that there may in fact be some meaning to some uses of the "K" hechsher. Moreover, I have found products with just "K" in a grocery store in a frum area in which they do not even sell non-cholov-yisroel milk. (When I asked whether the product was kosher, the frum man working at the store pointed at the "K.") So what's the deal? Is [some] food under the "K" hechsher actually kosher? What is the provenance of the hechsher, and how do I know what I can eat from it?