How can I remove a signature once it's saved in Preview.app?

How can I delete a signature that I inserted using Preview.app?

I can edit or delete all the text fields but the signature seems locked somehow.

A possibility is to try
File > Revert To > Browse all versions...

though I guess it will depend on how far back that version history goes. I've been unable to discover just how far back that would be & for how long it may be saved.

You cannot remove a Preview.app signature in Yosemite. This is a bug. It would almost make sense if signing a document froze the entire document,but you can edit every other annotation.

I've tried masking a signature with a filled box, then overlaying a signature on that. It seems to work and the document saves, but on opening tne new signature is gone. (Another bug.)

I was able to do it by using a rectangular annotation via Tools -> Annotate -> Rectangle. Make sure it covers the signature and just make the background and border match the color of your document background (white in my case).