1. Noticeable; distinguished from what is ordinary; eminent; remarkable; memorable; as, a signal exploit; a signal service; a signal act of benevolence. As signal now in low, dejected state As erst in highest, behold him where he lies. (milton)
2. Of or pertaining to signals, or the use of signals in conveying information; as, a signal flag or officer. The signal service, a bureau of the government (in the united states connected with the war department) organised to collect from the whole country simultaneous raports of local meteorological conditions, upon comparison of which at the central office, predictions concerning the weather are telegraphed to various sections, where they are made known by signals publicly displayed. Signal station, the place where a signal is displayed; specifically, an observation office of the signal service.
Origin: From signal, n., cf. F. Signale.