Note that these instructions are specific to using the signature in Google Gmail. Other mail clients can use the signature, the process is similar.
After applying the correct signature settings, copy it:
In a browser, open your Gmail account (mail.google.com) and from the upper right navigate to:
Settings > See all settings
Under the General tab, scroll down to Signature, and select the button:
+ Create new
Give your new signature a name, then paste the previously copied signature into the text box to the right. Adjust the Signature defaults to fit your needs, scroll to the bottom and select the button:
Save changes