In the process of creating a prop pilot's certificate I've discovered that there's an entire underground devoted to making high-quality fake documents. No, I'm not talking about traditional counterfeiters, but artists that specialize in producing incredibly detailed money and certificates. One of the best I've come across is Jerry D. Mills. Check out his mock Battlestar Galactica colonial bills.
Or these animal based designs for the upcoming "Zoovolution" online game.
He has more examples of faux currency in his gallery, as well as some inspired designs for unit patches and documentation.
I stumbled on Jerry's work while looking for help on recreating the fine engraving used on money and certificates to prevent counterfeiting. My Google-Fu was weak, so it took awhile to even learn that those swooping, repeated patterns are called guilloché. In the past they were scribed on printing plates using a specialized machine under the guidance of a master engraver. These days professional artists working in the high-security paper business generate them with specialized programs and plugins, but their basic look can be reproduced with an off-the-shelf program and a little effort.