Ever since Valve started seasonal sales, they've posted new artwork every day of the sale. If you have a fullscreen or low res monitor you might not notice it, but it's visible on widescreen monitors. The artwork generally tells a story using the Steam mascots (CyL [black dude with moon face], Tappet [orange dude with bobble head], Sir Roderick Bodkin [yellow dude], High-pockets [purple dude with tall skinny legs], Dash [the green fat whale blob guy]... there's also a tiny little dude with no limbs and no name).
Frankly, that stuff is more interesting that 78% off some $4 indie game you're never going to boot up anyway.