telltale

(noun) someone who gossips indiscreetly. Synonyms: tattletale, tattler, taleteller, talebearer, blabbermouth.

(adj) disclosing unintentionally. Synonyms: revealing, telling, telltale(prenominal). Examples: "A telling smile." "A telltale panel of lights." "A telltale patch of oil on the water marked where the boat went down."