Well buddy..i dnt knw abt images as ur siggies in Yahoo mail! but u can write TEXT siggies in Yahoo. U can do it with graphics as well..as there is an option of
PLAIN or COLOR & GRAPHICS For tat follow this:
Login to ur account and clik on the
OPTIONS tab (located at the Right hand top corner of the mail) then choose
PERSONALISATION in tat choose
SIGNATURES and then make ur own custom siggy..
And
check the box named as--->ADD SIGNATURES TO ALL OUTGOING MAILS and voila ! ur done.. with ur very own personalised siggy...
cheers n e-peace........