As I said, it depends on the site. Image sigs are quite important to users on gaming sites. Whilst some use the same sig image for a long time, many change theirs on a regular basis to reflect the games they are currently playing / favourite game. Others use image sigs from other sites with dynamic stats showing latest kills/awards etc.The best signature size is zero. I've removed signatures on my forum and not a single person has complained. Why would anyone want to see the same old signature over and over again.
signatures = clutter to the max