美国人在胸口画十字是为了表示一定会实现诺言或誓言。在胸口画十字这一手势可追溯到画十字这一宗教传统。现在罗马天主教和东正教的教会里仍然在沿用这一传统。人们相信借助这一宗教传统的力量，在胸口画十字可以使自己免遭厄运，并且也证实自己的誓言是虔诚的。因此有这么一句圣言警句：“我发誓，我宁愿不得好死”，也就是说，如果违背誓言的话。

Americans cross their hearts to seal promises or pledges. Crossing the heart goes back to the religious tradition of crossing oneself, which still exists in the Roman Catholic and Orthodox churches. It is believed that the gesture provides protection against bad luck by invoking the power of this religious tradition, and thus attests that the speaker's pledge is in earnest. Hence, the solemn caution:" Cross my heart and hope to die," that is, if the pledge proves to be false.