I have a lens in front of me that has me a little baffled. It is a "Wide Angle Portable Symmetrical" lens, with wheel stops that are not clearly labeled. A cursory search through all the usual sources shows that name to be most commonly associated with Ross, London. There is, however, no makers name on the lens. What is there is an inscribed letter "G" inside a diamond. I know I have seen this trademark before, but can't place it. Any help?