Now I Know: “…Back in the 1960s, the U.S. Bureau of Alcohol, Tobacco, and Firearms (ATF) began what is now known as the International Ink Library. The idea was simple: collect samples of pen ink from around the world for use in criminal forensics. In the 1980s, the ATF transferred control of the library to the Secret Service (which makes sense given that the Service investigates financial fraud as well as threats against the lives of the President and Vice President). Today, Secret Service agents collect pen samples from around the world on a regular basis. Whenever a pen manufacturer comes up with a new formulation, they provide a sample to the Secret Service. And currently-used pens aren’t the only ones they’re after — agents have acquired samples from most commonly-used pens dating back to the 1920s. In total, the Library has more than 11,000 ink samples in its collection, each one of which has its own unique “fingerprint.”…