Go to
https://meta.miraheze.org/w/index.php?title=Community_noticeboard&action=edit&section=new
and in the title, put ~~~~
and hit preview.

The preview shows ~~~~ but when you save the page, they become the
signature. BUG 1.

OK, do it again, but with <nowiki>~~~~</nowiki>.
Again, the preview makes you think it will still be ~~~~,
but when saving it gets expanded anyway. BUG 2.

The only thing one can do is use ~ ~ ~ ~ to keep it safe.

Seen on
https://meta.miraheze.org/w/index.php?title=Community_noticeboard&diff=101969&oldid=101968 .
But not present in
https://en.wikipedia.org/wiki/Wikipedia_talk:Sandbox .