I would guess that a significant portion of Signal's users are non-technical people dragged there by their technical friends that couldn't get them onto Matrix.
I would still guess that none is a bad assumption, however.
Edit: Spelling
Practically none. I think it's safe to assume it's not even 1 in 1000 who have registered with a VLN, or even know what one is.
You raise a valid point. I would think that probably more than 1 in 1000 would know, but suspect you are right about how many actually would do it.