http://dnbible7sqskwppgaqohboxz7u5kzffjzdx3lxzpjtt3s6tzeiytb5ad.onion/bible/darknetmarkets/how-to-verify-an-onion/verify_onion/index.html
It should come back with good signature at the bottom ,and at the top you will see a list of the current market mirrors. Make sure the address you are on matches one of the ones in the signed message. If it does you are on a official market onion! Once you do this a few times it really only takes about 10 seconds to do.