Does Pilate’s sign on the cross spell out the acronym Y-H-W-H in Hebrew?

No. Here is John 19:19 from the UBS Hebrew New Testament.

יֵשׁוּעַ הַנָּצְרִי מֶלֶךְ הַיְּהוּדִים׃

There is no V (and) in front of the Jesus The-Nazarene [And] King [of] The-Jews.