According to a comment, the Yukaghir love letter as semasiographic
communication was debunked by John DeFrancis in 1989 who asserted that
it was merely a prop in a Yukaghir parlor game. Perhaps that debunking
was in the very book cited by Martin J. Dürst earlier in this thread.
Martin J. Dürst via Unicode wrote,
>> There is a well-known thesis in linguistics that every script has to be
>> at least in part phonetic, and the above are examples that add support
>> to this. For deeper explanations (unfortunately not yet including
>> emoji), see e.g. "Visible Speech - The Diverse Oneness of Writing
>> Systems", by John DeFrancis, University of Hawaii Press, 1989.
The blog page comment went on to say that Geoffrey Sampson, who wrote
the book from which the blogger learned of the Yukaghir love letter,
published a retraction in 1994.