Hi B - I've bought a couple stones that are similar to this, but not enough to really research them that much. I've been more of a med-stone person of late, anyway. Vinster has bought some like this and maybe he could also weigh in with a thought. Maxim sells similar stones as Nakayama Maruichi I think, but I don't think you could ask him as obviously this isn't one of his.
It's an older finishing stone. I'm not going to make out all the kanji right now, but can look again tomorrow if you like as I like to solve these things. The stamps are saying it's a Kyoto toishi, good quality, honyama and a layered/slate stone, and so a finisher. I'd assume a tomae. There are stones like this around and I'm not sure how old they are, but they sell anywhere from about Y15,000 up to really high prices, depending. Not sure if people would buy these for tools or razors or knives in previous decades, but you can expect it to be harder or hard and a finisher. I think in the old days, and sometimes still now, it was normal to stamp stones a lot with these guarantees and affix stickers identifying the seller which, like the certified Sakai craftsmanship stickers on some knives, owners are reluctant to remove, or at least it seems important that they photograph stones for sale like this. It'd be described as 'vintage' no doubt and, oh, it's small in the top photo but I think I may see the Shoubu kanji on the stone which would give its specific origin if correct. I'm sure it's a good quality stone, but its value would depend on the price and what you want to use it for. PM me the listing link and I can take a closer look if you don't want to list it publicly.