Mysterious Conformance Mark

[calzap]

I'm familiar with most conformance, warning and advice marks on electronic equipment, but there's one that mystifies me. It's a white square with a black arc running through it from the bottom edge to near the right-hand edge. There are some non-revealing letters and numerals just outside one or two edges. I've seen it on several small DC power supplies. A pic is attached.

Anyone know what it is?

Mike in California