Hi fiberhome,
welcome to the Apple Community.
Sorry I'm no expert in this area.
Apple support have articles online that may help.
Create and use email signatures in Mail on Mac – Apple Support
Eg: Says:
"Delete signatures
- In the Mail app on your Mac, choose Mail > Preferences, then click Signatures.
- Select a signature in the middle column, then click the Remove button .
When you delete a signature from All Signatures, it’s deleted from any account that uses it."
If you still need help:
Something here may assist:
This shows the process you may have followed to set the signature:
Sign or encrypt emails in Mail on Mac – Apple Support
How to View the information stored in a keychain on Mac – Apple Support
Change Signatures preferences in Mail on Mac – Apple Support
An online article ("Use digital signatures for email") https://kb.iu.edu/d/bcsn says:
Disable your certificate in Apple Mail
- Open Mail.
- Begin composing an email message. Click the "Signed" icon (blue rectangle)
- ) in the lower right of the message header to no longer digitally sign email.
Hope something here works for you :-)
Else:
There is a "Get Support" link to Apple at top right on this discussion page.
OR
Apple phone numbers around the world
Contact Apple for support and service - Apple Support
All the best :-)