Someone sometime posted an image with a list of the 10 Arabic digits from a manuscript, which had two variants for "5", both with a tilde or macron above. Rene conjectured that the tildes could be two "v"s standing for "vel .. vel" (= "either ... or").
But on the bottom right corner of page You are not allowed to view links.
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So perhaps those macrons are just meant to avoid confusion with the letter "y", and the "mysterious symbol" on You are not allowed to view links.
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All the best, --jorge.
[KG: I could not find the post with those digits. If this post is out-of-topic for this sub-forum, feel free to move it.]