[jka]

Indeed, it's a very nice story, but appears to be fake. I won't duplicate what other commenters have added in this thread, but one other approach to investigating is to see whether any other images of Yukaghir semasiographic letters can be found online.

Perhaps this wouldn't be foolproof (given that the Yukaghir population is very small, and their materials might not have been published and indexed widely online) but the absence of any other examples certainly seems a little suspect.

Search link: https://www.google.com/search?q=Yukaghir+semasiographic&tbm=...