Telltale (noun)

A sign or indication that reveals the presence or existence of something.

Origin:

Derived from middle english words meaning 'to tell' and 'tale'.

Examples:

1. The dripping sound was a telltale of the leaky faucet in the bathroom.
2. The telltale signs of a heart attack include chest pain, shortness of breath, and sweating.
3. The redness and itching of the skin were telltale of an allergic reaction.
4. The sudden drop in the stock price was a telltale of the company's financial problems.
5. The strange behavior of the dog was a telltale of its illness.