The buildingsymbols appear to have a real function, even changing from red into green when a door works. So, I think also these are the originals. And also, they seem to perform a real funtion (go here-open-danger-working-offline). Likely thats why they are the most complicated designs.
The covenant seems to dotter them around like graffiti and badges, it looks more painted/sprayed. Maybe they assume taking on the symbols gives them sort of power/puts them in the forerunner camp. Or some sort of camouflage, belong to this current enviroment.
The humanstyle is usually more simple and maybe they fall in the same category as christian crosses, tribal tattoos, egyptian ankhs and political/industrial logo's, semi-religeous and graphical designed, looking 'cool'.
