When it comes to my forums index page, I limit how many graphics I have on the page as it can affect people loading up the page if they are on slower internet connections. Usually, I will have my logo, maybe some ads if I choose to have ads on my forum and I will also have the images for the read and unread on the forums. I do know that you are able to change the image for the read and unread on the forum index and I did do that once to have an image that represented the forums but some people found it slowed the site down if they had slower connections so I went back to the default.
I keep it low is that the page size is low otherwise it's more server load and not good for traffic like people loading it takes longer and more bandwidth