Almost 150 years ago, President Lincoln found it necessary to hire a private investigator - Alan Pinkerton - for protection. And that was the beginning of the Secret Service. Since that time, federal police authority has grown in depth, scope, and to a large number of multi-letter agencies - CID, OSI, NIS, FBI, CIA, INS, IRS, DEA, BATF, etc.
Now we have the "Federal Air Transportation Airport Security Service." Can't you see them now, these highly trained men and women in their black outfits with their initials in large white letters across their backs: