The 1931 Straits Settlements $10 P-18a is very popular design sought out by many collectors. It is very tough to source in high grades & yours is the scarcer of the two dates (1931). My guess (from the blurry/glaring photos) that your note is Fine to VF with 2 stains & graffiti. It is impossible to get an idea of whether the note was processed (washed or pressed) but if it is original I can imagine receiving $400-$600 USD for it (possibly more).
If I were selling it I would prefer to put it up for auction (1st route) unless I needed the money asap. If I were selling it in person, I would be stressing that it is the tough early signature (A variety) & be very reluctant to accept a lowball offer. Good luck!