I think it's a black sign with white lettering.

我认为它是一个写着白字的黑色广告牌。

youdao

As soon as Sally got home with her mom, she painted a picture of the park and wrote a sign in large black letters at the top of the picture.

莎莉跟妈妈一回到家，就画了一幅公园的画，在画的顶部还用黑色大字写了个标志。

youdao

Black clouds are an unmistakable sign of coming rain.

乌云是下雨的明显先兆。

《新英汉大辞典》

Yellow or brown areas shaped like the letter V on leaves may be a sign of black rot infection.

VOA: special.2009.03.03

In the nineteen forties, she was the first black woman to sign a long-term agreement with a major Hollywood movie studio.

VOA: special.2010.05.14

The race began after a moment of silence for the Boston victims, and many wore black armbands as a sign of solidarity.

NPR: A Look At Boston Marathon Bombing, Investigation

Since signatures can now be printed on correspondence, if you hand-sign with black ink, it may not be clear you actually signed it.

WSJ: Jan-Patrick Schmitz of Montblanc on Choosing the Right Pen

Thieves had cut up the black wrought-iron sign into its three constituent words in order to fit it into their getaway car after taking it down from the main gate.

BBC: Auschwitz museum unveils restored stolen sign