每个人的签名是独一无二的。

Each person's signature is unique.

《柯林斯英汉双解大词典》

现时标志是一个由发送方(签名者)新生成的无重复字符串，这样目标接收方就能检查其唯一性了。

A nonce is a non-repeating string freshly generated by the sender (the signer) such that the intended recipient can check its uniqueness.

youdao

我如果要求你在空中书写自己的名字，或用你的肘部、你的鼻子或是你的脚，大差不差，我们还是会得到你独一无二的签名。

I could ask you sky-write it, or make it with your elbow, or your nose, or your foot, and pretty much we’d get your unique signature.

youdao