Welcome to TFL, and kudos for taking time to read through thread(s) to try to find information! This is probably the single largest repository of hat information. While other more experienced members are generally most ready and eager to help, reading is highly encouraged and appreciated. The "M" stands for misto, which is mixed felt or heathered. If you do a search for "sodio" you will find several other examples of this combination. While dating a Borsalino can be somewhat challenging I think you are probably right placing this in the 60s. This is based on the serrated label without "Borsalino" included vertically on the left (which would have placed it earlier), as well as what appears to be a shorter brim width. I'm guessing it's 2" or less, though camera angle can be deceiving. Shorter brim widths are synonymous with more recent vintage hats, as this was the direction fashion was trending in the 60s and 70s. This is indeed an Italian market hat. Salvatore Balbi Napoli (Naples) was the retail shop. You will find quite a few hats on here (and in the wild) that originated from this store. Additionally, the size 4-1/2 was used for this market and is associated with the Point sizing system. This translates to U.S. size 7. As to value, that's somewhat difficult to assess since it's largely dependent on the taste of the individual end user. For many, vintage Borsalino's are probably considered the gold standard. Most collectors here prefer hats with larger brims, so this would affectionately be called a "stingie brim." Nothing wrong with it per se, just not as popular on the whole. That being said, others prefer these shorter brim styles. Somewhat similarly, a heathered finished is less common but not necessarily better or worse than a non-heathered hat. (For reference, I have a heathered stingie brim pork pie style hat made by another manufacturer in my collection, but it's the only one of that type.) Also, a self-felted "ribbon" is somewhat uncommon. Again, different styles for different tastes though I personally would probably consider a heathered finish a little more casual. As for size, back in its day it was probably average for its time. This is supported by the fact that many used hats for sale online today fall into the 6-3/4 to 7 size range. Present day average is more like 7-1/4, so if you're looking to sell you will likely have a smaller market. This is indeed a somewhat unique hat, so if it fits wear it proud. If you're looking to sell, you are probably looking at a more niche buyer given the characteristics of the hat. That may be good thing, maybe not. What I can say is that you got a heck of a deal for 25¢!