The suns in the art refer to the storyline element of the dawning of Mirrodin's green sun, while helping you remember the multicolored orientation of these artifacts with Sunburst.
Even those cards that depict closeups of small artifacts manage to sneak the five suns in there somewhere. For instance, take a look below at this zoomed-in art of Pentad Prism. You can see the five suns reflected in the surfaces of the magical prism.
Pentad Prism
Pentad Prism and the five suns of Mirrodin - Art by David Martin