They're not Chinese characters. Some British officer swords of the period were "blue and gilt," that is ornamented with dark bluing (a kind of oxide coloration, accomplished either through heat treatment or chemicals, which helped to protect the blade from corrosion and/or served as a nice dark background for additional ornamentation) combined with etching and gilt (i.e. gold chemically applied) to the etched figures. In practice, at the time gilding and bluing were often accomplished together with a single heat treatment. You can see an example of a sword with similar ornamentation here

It is to be remembered that during this period officers in the British military purchased their own swords (as opposed to NCOs and troopers, who were issued their weapons), and they could get quite fancy indeed, and the exact blade style could vary considerably between officers. In the full painting, you'll note the basket-hilted claymore of the fallen officer on the right, which taken with the tartan suggest a Scottish officer. On the left, the two officers with blades unsheathed show that they are free of ornamentation, signaling that they're probably lower-ranked (or at least, not quite as wealthy) officers.

For more information on the subject, I'd recommend Ewart Oakeschott's European Weapons and Armour and British Military Swords by Stuart Mowbray.