I have lost the signatures in Apple mail. Thaey are still there I can see them. How can I assign them to the appropriate mail address.? iOS Mojave Mac Mini.

It is not so clear what your issues is...

Mail>Preferences>Signatures

If you see your "signatures" in ALL Signatures—from that window, drag and drop from the list to the email account you want to add.

from the example you see I have 5 signatures—I have dragged 4 of those to my Dominant account window.

Now you should have a sig option in your email:

Hi sheldonwg,

Welcome to Apple Support Communities. I understand you're unable to use email signatures in the Mail app on your Mac in macOS Mojave. I can help point you in the right direction.

If you're looking to automatically add a signature to your emails, I recommend following the section in this helpful article that says, "Automatically add a signature to emails": Create and use email signatures in Mail on Mac You can add the signature to your emails manually by follow the next section that says, "Add a signature to emails yourself."

For any reason you continue to experience the same behavior, I suggest deleting the signature and to re-add it by following the article I provided.

Kind regards.