An American crayfish, Pacifastacus leniusculus, having a large claw that it waves to attract a mate.

Alternative spelling of smoke signal

(often pluralized) A method of long-distance communication sometimes used in ancient and undeveloped societies, consisting of messages conveyed by means of columns or intermittent puffs of smoke.

An event or emanation to which a sensing device gives an undesired positive response.

An unclear message, often contradicting a situation.

(US, telephony) An audible signal to the calling party that indicates failure to complete the requested connection; an engaged tone

A transmitter encodes data by producing a signal which is a continuous stream of signalling events each which has sufficient information for the receiver to recover the original data. Just like a quantum leap is the smallest measurable leap, a signalling event is the smallest possible amount of signal that the receiver needs to recover the original data without error.

Alternative form of time signal

plural of signal box

A building, typically adjacent to or spanning a railway line, from where signals, points and (sometimes) level crossings are controlled. / The alarm-box of a police or fire-alarm system.