Some editors, and some wikis, have strong views about the "correct" way to sign a comment. Early Wikipedia conventions were similar to USENET e-mail conventions, with a pair of hyper-minus characters indicating the separation point between content and signature. These often map with how (in)convenient typing tildes are on their keyboard, because the signature button in the 2006 and 2010 wikitext editors includes the pair of hyphen-minuses, while people who type the tildes directly don't bother typing the hyphen-minuses.
As a result, there are at least three common signature styles:
Most editors at most wikis: ` ~~~~`
Some editors at most wikis: ` --~~~~`
Most editors at some wikis, especially jawiki and cswiki: `--~~~~` (no space; the "period" is U+3002 and contains the space.)
It might be good, at least at wikis where a convention is strong, to be able to set the default.
Reported by User:ネイ at https://www.mediawiki.org/wiki/Topic:Vk5r8qy9o799ucnw