http://wikipewt4n75trifcse2ggaieot27svognl7idu6xmmqn37kf64rvsyd.onion/index.php/Verifying_PGP_signatures
Trusting the key Instead of a yellow warning, you may want a positive confirmation with a green box. That is only possible by signing the key directly, or by establishing a web of trust (by signing several other keys, usually three, that already have signed this key).