1) Have a Signature
2) Click the Sign button
3) Click the little minus button next to your signature
4) The signature is immediately and irrevocably deleted.

This also works for Initials.

Need a confirmation window, or the ability to undo the deletion.

If I didn't have a scanner handy after accidentally doing this, I would be royally screwed right now.

(I have not investigated whether this behavior is configurable, but even having this as a default setting seems like a very bad idea)

Adobe Acrobat Reader DC
Continuous Release version 2020.012.20048
Windows 10 Home x64