Comment 33 for bug 772709

Never Follow (neverflw) wrote :

Confirming that the bug still exists in Lubuntu 13.10, as far as the nm-signal*secure.svg files are concerned for the default Lubuntu theme.

Workaround as above (#18); note that the default theme seems/is 'Lubuntu', so use that theme as basis:

sudo cp -a lubuntu <new theme directory>
cd <new theme directory>
sudo vi index.theme
sudo cp ../Humanity-Dark/status/22/nm-device-wired-secure.svg panel/22/

Lastly, choose the modified theme in Preferences -> Customize Look and Feel.