I guess I'm not looking specifically for an icon, just an idea of what I could use for imagery. I'm having issues today (probably that double cappuccino) imagining what kind of image i could use for something that demonstrates the capability to toggle the idea of "apply all [filters]" and "remove all [filters]". The image doesn't have to show both, just one or the other, and it would switch based on the state.
Of course if you have an icon (16x16), that would be great :) But really I'm just looking for ideas. My current icon set is basically the FamFamFam silk set.
Icons are guaranteed to confuse most people when used in isolation. I completely love the way Firefox icons have text when there is space to have them. So try and think extra hard about whether there's any way to have a text label next to the icon.
As for the icon, what about 3 overlapping filter icons?
But, taking a step back, Can you break the task into 2 operations -- select all then apply selected filters? I don't know the context of your work but if you can select more than one filter then this might work well. Certainly lots of apps do it.