The four names (presumably all surnames) are printed at the top of all abstract pieces of paper throughout the first and second series.
The names are printed on pieces of paper in different books, including the Black Book of Buried Secrets, The Cahill Files 1 to 4 and the booklets which come with card packs. Only one of the names is known - McIntyre, surname of William McIntyre, one of the longest running characters.
The paper suggests that the other names are people who William used to work with, however there is no information ever given in the stories about them. This makes it unclear if the people are still alive, and if they are good or bad.
Some people thought the names were just for decoration on the paper, but when they were featured in the Cahill Files, the letters written by Clifford Riley mention the Cahills past.
Is it possible that these people are Vespers? Or maybe Cahills? Book 6 is going to release more information on all the characters, Cahills and Vespers, so hopefully more should be explained.