It would be interesting to see a graph of a soundtrack of different people speaking this word to see whether it really is one syllable.

I don't really think that would solve the problem. I've spent some time looking at spectrograms of speech, and it's difficult to tell much from them. I'm not aware of how to determine syllabicity using them. If it were easy, phoneticians wouldn't be arguing or worrying about what constitutes a syllable.

Ceci n'est pas un seing.