I was looking for the form name of the main Service Manager sign in page, i've attached a photo of the page in question.
There is no form for the login page. And if you want to do the rebranding, in 9.4x, you can do it by change the settings in tailoring-> rebranding. And in 9.3x, you need to change the jsp/css files in the webtier which will cause conflicts when you upgrade the webtier.
Let me know if it helps a bit,