The international food company Pampa sells a tin of herring fillets in oil, but I do not recognize this symbol on the back and cannot find information on the Internet of whether this is actually a hechsher.
As you can see near the bottom of the pictures, there is a crown with the letters "PL". This fish is listed elsewhere on the package as a product of Poland. I would seem reasonable that this would then be the hechsher of local Polish rabbi, certifying this fish for consumption, but I cannot kind this "Crown PL" on any lists of international kosher symbols. It may mean something else entirely. Does anyone know anything about this symbol?