Signatures are separated from the rest of your message by two dashes. To see a signature in Gmail, click the Show trimmed content button at the bottom of the message.
When you reply to an email, your signature is added to the very end of the message, below the quoted text of the previous messages. However, you can change your setting so that your signature appears above the quoted text. This setting also removes the “--” above your signature.
To change your setting, check the box next to “Insert this signature before quoted text in replies and remove the "--" line that precedes it” under the signature text box on the Settings page.