I've looked everywhere (with the exception of in the forum history, but it shouldn't be buried as I think it's important), and I can't seem to find out what the components of the gate level icons mean. I figured out that the background color = the element of that section of the level, and the color of the icon represents the monster type (verification needed?), but what do the gear and monsters icons mean? I know it has something to do with the type of level (shield for arena, clover for treasure, grave for graveyard).
I think some kind of instruction in the game (preferrably in the bazaar or accessible from the gate map menu) would be awesome, especially for new players who are confused. Thanks.
The wiki is quite useful for information about the game (big wiki button at the top of the page)
http://wiki.spiralknights.com/Gate
That link should help answer your question.