Plain "K" is not necessarily the Mass. Vaad
Someone posted back in Nov., regarding Arnold's bread that the "K" is the Mass. / New England vaad. In fact, the "K" is just a generic symbol that can be applied in different ways. It can stand for a known kosher agency that the manufacturer does not want to display for certain reasons, as in the case of Kelloggs. And it can be applied legally, even by a non-Jewish outfit that is not supervised by any kosher agency, but claims the product is kosher according to their own standards.
To the person who posted that "K" is acceptable - you may want to be in possession of all the facts before you post advice in a public forum.