My signature disappeared one day and now cannot upload a new jpg or png to put my signature back in and have saved. Keep getting error message that my files are corrupt. I have macOS Tahoe 26.2.

If you're getting a message that the file is corrupt, then the file is corrupt. File corruption is always, no exception, caused by hardware failure. Common causes are saving directly to external storage and/or over a network connection (both unsupported), or just a drive about to fail.

What is the exact message?