Long time ago, I, as Cyberwarrior (I've lost access to that account) created a topic here where I asked what would ranks and insignia for the armed forces in a world government would look like. Apparently, the topic was deleted, as I linked images from imageshack.us in a way which no longer works.
I made some sketches and our own Medic_in_Uniform came up with some awesome versions of those insignia, which I thought it was a good idea to make available at this forum again.
Army (green), Air Force (Air Force blue), Navy (Navy blue) and Space Fleet (gray):
Uniforms (for the five services):
Uniforms (for Naval Marines):
Uniforms (for Space Marines):