Nice sword, Tim. Congratulations!
I've never seen that blade marking before, so I can't help you there. As for the origin, I believe this is in the Thai style (we're revisiting the rough typology we started a few years ago, and the tribal nomenclature is less helpful.). The handle/blade proportions and the stylized lotus-bud pommel make me think this, although these features do appear on swords from other areas in the region (long handles often apear on Laotian swords, and variations of the pommel appear on Burmese swords as well). I'll let Mark address this more definitively, as he's really doing the heavy lifting in our research.
Age is a tough one, particularly from photos. This thing looks pretty old, but in nice condition. I'd say late 19th/early 20th century. It may be older.
The blade is nice, and that broad central fuller is not rare on Thai swords. The blade tip is interesting, and it looks like the fuller extends all the way to the end? Any chance you could post a close-up of that feature?
Best,
Andrew