The first signal did not include the color yellow for caution, but that was later added within a few years.

第一次信号中不包括用于“ 注意”的黄色，黄色是以后几年内后加的。

youdao

The first trial in the 1830s, that of choosing green for the caution signal, and clear for the go signal, failed miserably.

第一次试验是在十九世纪的三十年代。起初他们选择绿色作为“注意”信号，明亮作为通行的信号，结果遭到惨败。

youdao

Marituu says this should serve as a caution signal for all historians.

VOA: standard.2009.12.25

Though the AAII Sentiment Indicator can be viewed as a contrarian signal, I would caution against relying on any one indicator as a sign that the market is at a turning point.

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But outside of providing him with a brick wall for an offensive line, any promise to keep the signal caller healthy should be taken with caution.

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