That is a very interesting mark. And I see that it has a dust cover underneath the seat. Very unusual. The stamped number, is it 109? Any others? That does not look like the sort of thing that would be on a handmade piece. But it looks like fairly low volume, high end production.
I would also guess that it is newer than the 1960s, possibly very new.
I'm guessing it's fairly recent. The dust cover is non-woven synthetic fabric so unless it was replaced later, the chair isn't 50s-60s. But the mark looks like the kind of breezily casual style graphic that became popular in the 90s, meant to look like it was dashed off by hand with brush and some ink.
The weaving looks like the warp and weft strands might be bonded together to make a wide, flat band of 8 strands. Is this the case? Because if it is, then there would be messy cut ends stapled underneath that they wouldn't want showing.
What is the history of the chair? I think your best bet may be to try to determine something of where it came from so you can narrow down where to look for that mark. I mean, even in the worst case scenario for lack of history, if you found it in the trash, it would be the trash in front of a certain building with certain people in it of certain professions, certain socio-economic background, in a certain neighborhood, and in a certain country.
And based on the colors of the wood it looks possible that it _could_ be cherry and weng̩, but it might help to actually confirm that with some closeups of the wood. Are the pegs of the same wood as the arms?
If you need any help, please contact us at – info@designaddict.com