What's a good icon to represent a legend or a key for a diagram?

Question

I'm implementing a small web app widget that shows a legend/key for a diagram (or chart/map/graph/whatever), but only during mouseover of the widget. It's basically just going to be a div with a background image. What would be a good icon that communicates "I show the legend" or "I am the legend" to the unfamiliar users? I'm looking for something in the 10x10 to 20x20 pixel range.

Assuming that a legend is the same thing as a key (is it?) then I could use a small icon of a key (like you'd unlock a door with) but that seems cheesy or unclear at worst. I'm not sure that's really the clearest way to do it. Is there an icon that should instantly remind users of a legend?

Answer 1

In my region (southern USA) I would say the key is better known then legend. Thus I would find an icon of a key for this. There are many Icon sites one that I frequent is http://www.iconfinder.net/

Answer 2

Maybe just a question mark icon - help / legend are kinda similar on a map.