The signal flag is fully in our sight from this position.

我从这个位置完全可以看到信号旗。

youdao

A fox USES its tail (or "brush") as a warm cover in cold weather and as a signal flag to communicate with other foxes.

狐狸用它的尾巴(或“毛刷”)在冷天时盖上保暖，同其他狐狸交流时亦可用来做信号旗。

youdao

Then the rain came and the red flag went up to signal a halt.

当时，雨下了起来，红旗被升起，发出停止的信号。

《柯林斯英汉双解大词典》

Generally, a bearish momentum divergence is a red flag warning signal, which often presages a pullback or correction.

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Their idealised version of this question was to ask how two signal chemicals, starting from opposite ends of an embryo, could result in a pattern that looked like the French flag (ie, three different coloured vertical stripes).

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