Anyone with the signature link can sign the card — that's the point. Occasionally you'll want to remove a message that shouldn't be there.
Remove a signature (office staff)
The message is deleted immediately. There's no soft-delete; treat this as permanent.
[Screenshot: Card detail page with a signature hovered and the trash icon visible]
Remove your own signature (signer)
If you signed the card and want to remove your message, hover it on the signature page and click the trash icon. You need to be in the same browser you signed on.