When posting a MassMessage to a Flow page, the four tildes do expand to a signature. See an example in the first post here:
https://he.wikipedia.org/wiki/%D7%A0%D7%95%D7%A9%D7%90:Sh8futgqnvmfktkk
The expansion is correct, but it sounds like a somewhat odd corner case, so I figured I should post it here.
Feel free to close as invalid if it's intended.