Where do I find the Mail signature file on my Mac

I did an update to my iCloud storage and now have none of my signatures for Mail. The names of the signatures are there but the content is empty.

I can probably recover them from my recent backup. However, what is the file and where do I find it?

I would like to avoid redoing all the signatures.

I'm running macOS 10.13.16 on a MacBook Pro.

Thank you in advance.