This is perhaps a long-shot, but I believe the paper that architects use is called "an arch" and is given "an arch" letter, depending on its size. Could the answer you are looking for be "arch E" or ARCHIE?
With respect to iamblue, it seems that Arch E is rather larger than 6 x 3 (36 x 48" in fact). There is a lot of info on paper sizes if you Google, particularly on Wikipedia, but at a cursory glance, can't find a name for 6 x 3. Good luck.