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I believe they are encrypted in your keychain. Just search "signature" in the keychain app.

Thank you. I did find a signature keychain in there but it didn't actually transfer my signatures when I imported it onto my new Mac. :confused:
 
Update:

I've figured it out! Here it is in case anyone wants to know where the signatures are stored. :rolleyes:

/Users/USERNAME/Library/Containers/com.apple.Preview/Data/Library/com.apple.Preview.signatures.plist
 
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