A machine or contrivance for indicating or recording something, particularly for keeping a check upon employees by revealing to their employers what they have done or omitted
Revealing something, especially something not intended to be known
Esimerkit
The telltale was the lipstick on his shirt collar
His eye was blinking, a telltale signal that he was lying
He blushed when he approached, a telltale sign that he was happy to see him