There are at least three problems here:

• This edit: https://en.wikipedia.org/w/index.php?title=Wikipedia:Village_pump_(technical)&diff=prev&oldid=1100545071 added <span data-dtsignatureforswitching="1"></span> to the page. This should never happen, it's an internal marker used in reply tool and it should be replaced by a signature when saving.
• Visual diff understands that markup and tries to render it as the viewer's signature, like the reply tool would. It should not be treated as a signature outside of the reply tool.
• When trying to render the signature (technically a transclusion of ~~~~), we call ve.init.target.parseWikitextFragment but ve.init.target is undefined. It should not depend on that (see T305762).

We're going to start by taking a look at the first issue @matmarex identified in T313809#8105017:

• This edit: https://en.wikipedia.org/w/index.php?title=Wikipedia:Village_pump_(technical)&diff=prev&oldid=1100545071 added <span data-dtsignatureforswitching="1"></span> to the page. This should never happen, it's an internal marker used in reply tool and it should be replaced by a signature when saving.

We previously had a task about certain operations resulting in <nowiki><span data-dtsignatureforswitching="1"></span></nowiki>: . But this one is without <nowiki> and is probably a different bug.

I wanted to find out if this is an isolated incident, so I searched: https://en.wikipedia.org/w/index.php?search=insource%3Adtsignatureforswitching&profile=all which gives 15 cases of dtsignatureforswitching appearing in pages. I looked up the edits (using http://wikipedia.ramselehof.de/wikiblame.php), and tried to figure out what happened.

There seem to be three kinds of ways for <span data-dtsignatureforswitching="1"> to appear:

• Kind A: <nowiki>...<span data-dtsignatureforswitching="1"></span></nowiki>. This was already reported as T280068. It happens when:
  • You input <nowiki>~~~~</nowiki> in wikitext mode (e.g. because you were explaining to someone how to add a signature), then switch to visual mode
  • You input ~~~~ in visual mode and prevent it from turning into a real signature (by pressing Ctrl+Z after the conversion, or by copy-pasting it rather than typing), then switch to wikitext mode (resulting in <nowiki>~~~~</nowiki>), then switch to visual mode again
• Kind B: {{...|...<span data-dtsignatureforswitching="1"></span>}}. This is actually quite similar to the above, but I didn't think about it before. It happens when:
  • You input {{...|~~~~}} in wikitext mode (where ... is any template), then switch to visual mode
• Kind C: <span data-dtsignatureforswitching="1"></span> without any other markup. I found one other example of this, but I still don't know how to reproduce it (except by doing one of the above, and then changing the markup in wikitext mode).