telltale

1. (figuratively) Something that serves to reveal something else.Examples: "The telltale was the lipstick on his shirt collar."; "It supplies many useful links and tell-tales."; "In most cases the event is shielded by a large mass and only telltales arrive on earth. Such telltales include neutrinos, or even some form of radiation."figuratively

2. (music) A movable piece of ivory, lead, or other material, connected to the bellows of an organ, whose position indicates when the wind is exhausted.

3. (nautical) A length of yarn or ribbon attached to a sail or shroud etc to indicate the direction of the flow of the air relative to the boat.Examples: "The sailmakers mistake can be an excellent way to lose a race as the telltale signals were disturbed and confusing."; "If you turn toward the wind, the sail becomes undertrimmed, and the inside, or windward, telltale starts to rise and flutter as the flow is disturbed."; "The telltale shows if wind is flowing across the sail on every point of sail except a run."

4. (nautical) A mechanical attachment to the steering wheel, which, in the absence of a tiller, shows the position of the helm.

5. (nautical) A compass in the cabin of a vessel, usually placed where the captain can see it at all hours, and thus inform himself of the vessel's course.

6. (engineering) A machine or contrivance for indicating or recording something, particularly for keeping a check upon employees (factory hands, watchmen, drivers, etc.) by revealing to their employers what they have done or omitted.