Answer:
   
   You'll have to keep informed. Note that in most states, "K" does not
   necessarily mean that the product has rabbinical supervision, so you
   can't rely on the simple K. Of course, many products with a "K" are
   kosher anyway, as are many unmarked products. The circled-U,
   circled-K, K-in-a-five-pointed-star, and k-in-a-letter-chaf are widely
   accepted nationally-known kosher symbols. Other accepted kosher
   symbols are only found in small local areas.
   
   In the Periodicals Reading List, you'll find a number of magazines
   focused on Kashrut. These magazines often publish information on who
   is behind the various hechshers. In particular, every year, Kashrus
   Magazine publishes an index to all the Kosher symbols and the people
   behind them. You can reach Kashrus Magazine on the net at
   (<[5]http://www.kashrusmagazine.com/>).