That's a serious case of Google-Image-Searchitis. My theory: somebody googled for "settings icon", swore to himself to get proper artwork later, forgot, and there we have it. (Yes, I'm guilty of that too, but I usually don't forget)
Sounds like this is a people problem, not a technical problem.
My point is exactly that you shouldn't have to. If all your license information sat in the files themselves checking licensing would be accomplished by adding a few standard lines to your deployment script.
If your website used Creative Commons-licensed media your CMS would even be able to generate attribution data to be shown at the bottom of the pages that use that media on its own resulting in fully automated compliance.
And totally unnecessary too, probably. I seriously doubt this kind of software is in any way an edge over their competitors - it's probably just big corp habit.
[settings icon]["settings icon"][free settings icon] etc don't return it.
Iconfinder is one the most popular ones around... so probably whoever is "responsible" for it used that kind of search engine.
There it is: http://www.iconfinder.com/icondetails/8844/128/kit_settings_... with author, licence and all the info.
We care a lot about stating the license clearly since it's essential to our business. Also if there is anything copyright infringing on our site we'll remove it immediately. As far as I can tell, this icon is created by the Oxygen team and the license information is correctly presented on our site.
If you know you were used for this, you might be in a position where you could choose to help out. There may well not be any clear evidence you were used in this instance though.