I am trying to use a numix icon for rxvt-unicode. I haven't found much recent discussion on this topic but the thread I was following was:
https://bbs.archlinux.org/viewtopic.php?id=166210
my /.Xdefaults looks like:
URxvt*iconFile: /usr/share/icons/Numix-Circle/scalable/apps/xterm-color.svg
when starting URxvt through my current terminal with rxvt-unicode I receive: "urxvt: Loading image icon failed, continuing without."
I was able to pretty much fix my problem. I made edits to the rxvt-unicode.desktop file changing the icon to one of my choosing. At that point I was able to see the new icon when loading rxvt-unicode from the unity launcher or sidebar. Information on finding the .desktop files can be found here: How can I find *.desktop files?
One thing I noticed though is if I use another terminal to launch rxvt-unicode it still shows the old icon. Not sure yet why that is happening. This only has become a problem because I created a keyboard shortcut to make Super+q launch a terminal and it does that through the terminal as far as I can tell.