The more I look at the marks on the item, the less I like them. If you look at the large letters "CS" the patina evident on the remainder of the surface is lacking inside at least parts of those letters. In the smaller stampings underneath, the first and third letters are obviously missing patina. I'd have to guess that the marks were put on the piece in recent years, probably no further back than 20 or 30 years, or their patination would match that of the surrounding metal.

Here's a part the picture that I blew up a bit, and enhanced the contrast on, digitally. I did all the digital enhancements to the whole picture, so there's no "doctoring" of one area vs. another, it was done uniformly to make the lettering easier to see.

If you could post a well-focused close-up of lettering, it would help.

I'm sorry to have to report my misgivings about the markings on the item, and please don't shoot the messenger! Also keep in mind that I'm only a layman collector expressing an opinion, I'm not an expert of any kind.