I have seen this orange icon before in the bottom right corner of the Firefox browser. It does not solely represent RSS or XML or Atom but all of these different types of feeds at one time. As Jeff Jarvis mentions in his recent post:
"...there’s a movement rising to replace both XML and RSS icons with an acronym-free icon that has been adopted by both Firefox and Microsoft."
It appears Steve Rubel adopted the new icon on his redesigned MicroPersuasion blog. The Technology Evangelist also has a similar and equally effective implementation. Somewhat Frank offers a number of different options however I am considering switching to to something similar soon, since my can be sent to my FeedBurner feed page and select the type of reader they use via a dropdown anyway.