Comment 18 for bug 772709

Here is what I did to fix it. I only use VPN on the wired connection. I guess a similar approach will work for secure/VPN over wireless.

cd /usr/share/icons

# Make a copy of the existing icon theme
# "pvm" is me. Invent whatever name you like here
sudo cp -a elementary-xfce-dark pvm
cd pvm

# in index.theme, change the "Name=" field to something descriptive for you,
# e.g. "elementary Xubuntu dark - with nm-device-wired-secure"
sudo vi index.theme

sudo cp ../Humanity-Dark/status/22/nm-device-wired-secure.svg panel/22/

# Optional step
# If you don't like the looks of panel/22/nm-device-wired-secure.svg, edit it.
# I made it lighter to fit the rest of the theme.
sudo chmod a+w panel/22/nm-device-wired-secure.svg
inkscape panel/22/nm-device-wired-secure.svg

sudo gtk-update-icon-cache .