Thank you so much for your kind note!
I have looked at this a number of times, and honestly between my glasses and my computer had not noticed a date. The pair of stamped markings are puzzling, and honestly I cannot see any similarity to a crown as Denis has suggested, nor any other particular image.
I do know of course that this appears to be an Ottoman type sabre, and that similar circular cartouches like these appear on some Ottoman blades. It would appear they are possibly arsenal acceptance or proof stamps, but they are not makers marks. A similar cartouche with illegible Arabic characters are seen on a nimcha blade in 17th century Algieria and placed on one side of the blade near the forte (Briggs, 1965).
The signature is as noted, spuriously, but perhaps patriotically placed with the name of Cossack Hetman Ivan Mazepa (1639-1709, born Jan Mazepa Kolodynski) who was with the cossacks of Left Bank Ukraine (Livorberezzhya) on the east bank of the Dnieper R. The term 'Left Bank' appeared around 1663. Mazepa was Hetman of the Left Bank from 1687-1708.
Apparantly he had fallen out ot favor with Russia, and at Poltava (1709) he sided with Charles XII of Sweden against Russia in fighting for Ukrainian independance. This resulted in a great deal of disdain against him by Russia of course as well as the Russian Orthodox Church and his alienation in Ukrainian history. During the 18th century, those who opposed the Russian government in Ukraine were known as Mazepintsy, or Mazepists. Perhaps this spurious signature alludes to this in a slogan type manner. The date by the same token perhaps 1663 or 1665 to the formation of the Left Bank Cossacks in the Ukraine. It is notable that Mazepa's father died in 1665, but uncertain of how they may apply to inscription on sabre.
As to the Ottoman sabre, Mazepa served as chancellor diplomatically to the Ottoman Empire. Ottoman weapons were also well known among the various Cossack hosts.
These are the only plausible clues I can offer to these features.
Denis, I hope I have somewhat accurately recounted this history, which of course you are much more qualified to describe. I am not familiar with the reference you note R. Gardner, can you say more?
In the attached, the map, in Russian, shows the Left Bank in gold; the coat of arms of Mazepa; illustration of Ivan.