What if we post here our concepts designs for armors, weapons, guild emblems, banner types, interface windows, special event skins etc.
You don’t need to be a graphic designer or a concept artist to post in here, a simple sketch can be enough to give an idea of what you think about
Also, if you find interesting designs on the internet, you can post them too so that ANet will have all ideas gathered in one place
Here is what I have found for a legendary rifle 
