Preview.app // Where Do I Find a Signature File?

Preview does not store a graphics file containing your signature. The signature is presented for you as a convenience. The signature is stored in some Preview preference location as non-image data that it can reconstruct as a signature image.

If you need a Preview signature in another application as a graphic file, you should insert your signature from Preview onto a white-space area of a PDF and then perform a Screen Capture of that signature.

vatolin wrote:

I am very convinced that this behaviour is not GDPR compliant. My signature is my own personal data. I am convinced I am entitled to get a copy of it in appropriate electronic format.

Then get a digitizer tablet and generate an image of your signature.

Apple's Preview has never provided a signature image file in the decades since macOS was first offered.

It's highly encrypted in Keychain, but to use it in Preview, click...

Tools>Annotate>Signatures, then it or them should show above the Manage Signatures...