As soon as it was dark, Mrs. Evans gave the signal.
天一黑，埃文斯夫人就发出了那个信号。
《柯林斯英汉双解大词典》
2
Many have never been studied, leaving scientists in the dark about the potential threats and the meaning of their Morse code-like flashes that signal everything from love to danger.
University of Chicago cosmologist Juan Collar believes his group may have spotted a dark matter signal in their detector inside an abandoned mine in Soudan Minnesota.