Recently I’ve create icons for GTK and I’ve notice strange thing. If you put this comment:
<!-- icon is vector for gtk Copyright (c) You should have received a copy the GNU General Public License along with this program. If not, see <http://www.gnu.org/licenses/<. -->
In svg file between xml prolog and svg root node, the file will not display in Nautilus. The same things is with icons.
here is link to example file.
This was tested on Fedora 14 64bit liveCD on VirtualBox