This is the image that my placard is enlarged from — notice the copyright that is in the lower left corner.

The website where these materials are studied in detail is http://zfacts.com/p/318.html, but this graph is merely a restatement of the National Debt as a % of GDP as supplied by the Treasury Department, the IRS, and many other government publications.

Those who wish to reproduce my placard can use this enlarged image, print it at Staples, Kinko's or the like as a black & white engineering print (under $5) and color in the colored lines by hand.