Bypassing the station's comm system so that their signal wouldn't alert station personnel to the incoming transmission-and then following that system to the correct companel-took a bit of finessing.
It was the cup he had almost broken the night of Zen Godo's supposed death; the signal they had agreed upon that would alert her, in another room, to his presence in the darkened house.
The signal would alert Lady Oyasa without carrying warning to any ears that might be listening.
Such anomalous signals might alert the Talin to the fact that an alien spacecraft is moving through their system at an appreciable percentage of lightspeed, which would, of course, be a violation of the Prime Directive.
A signal from his console alerted him that Sagan was approaching Ezri's location.
The next wake-up signal, AAA - encrypted, of course - would alert them to go to periscope-antenna depth to get more detailed instructions from SSIX, the submarine satellite information exchange, a geosynchronous communications satellite used exclusively by submarines.
Using those cases, the F.B.I. plans to develop a computerized system to identify signals to alert them to problems in an agent's relationship with an informant, based on things like the length of the relationship and the money paid.
However, a wrong signal sent from shore alerted the U-boat, which dove and escaped.