I am using a Mac Pro (mid-2010) running MacOS Mojave (no tracking pads or cameras) and could not export a signature file from my Macbook Air (mid-2013) on MacOS Sierra.
I've tried the old process of copying the file com.apple.previewLegacySignaturesConversion.plist along with the keychain password and pasting it into my Mac Pro. Subsequently, a signature annotation privacy (which did not exist yet) was created for the Preview application (with the keychain password) for the copied file above). And it did not work. How can I solve this?