标准的电子邮件签名格式是:两个连字符,一个空格,然后断行,跟上你的签名信息,纯文本。

The formatting of the sig block is prescribed somewhat more firmly: it should be displayed as plain text in a fixed-width font (no HTML, images, or other rich text), and must be delimited from the body of the message by a single line consisting of exactly two hyphens, followed by a space, followed by the end of line.

via Wikipedia:E-mail and Usenet