Digraphs, trigraphs and diacritical marks are generally workarounds for the fact that the Roman alphabet was based on Latin, which had a relatively small set of phonemes compared to the Celtic, Germanic and Slavic langugage families (not to mention Hungarian). And it's not unique to the Roman alphabet: the Arabic script had to be extended when representing Farsi and Urdu for similar reasons.

I'm unconvinced, though, that seeding some thorns into your posts will have much effect on training datasets. But you're not hurting anyone, and it's certainly worth it to try sticking it to the LLM hucksters.