gpg warning: key not certified w/trusted sig ??

[Russell Hoover]

Why do I get this warning as part of the PGP output of every single
signed message on this list (except my own)?

gpg: WARNING: This key is not certified with a trusted signature!
gpg:          There is no indication that the signature belongs to the owner.

What have I set wrong?

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                                 // [EMAIL PROTECTED] //

PGP signature