I am using blogger, for blogger I think you go to Setting - Formatting - Post Template, n paste HTML in the box... It works, but I am not sure if you do mobile blog... It seems the signature comes on top, if you blog from the computer, then it won't be a problem, but I don't think you can control that from mobile device... I hope it helps you though!
You can create an image with a nice designed signature and add it to your template... There are many places you can use and most are for free.. Hope I can tell you which one I used but I don't remember and neither I saved the link :( Can't wait to see yours! :)
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