How can I add a logo to my signature in Yahoo mail?

Using Yahoo! Mail how do I add a signature to some emails and not to others?

• The box to check "add my signature" is not at the bottom of the compose email...nothing is there. There was a timeline there but I checked not to display it, hoping the box to add my signature might show up. I am using Firefox 2.001.

• Answer:

  if you are using yahoo beta,first you need to have a signature ready.If you do not have, go to options,click on compose,and select 'show signature on all outgoing messages' When composing a new message ,the signature will be SHOWN in the compose text box ,if you do not want to use it,select it and delete it.