What Does This Symbol Mean?

Sometimes, the online questions we get through “Ask A Librarian” are harder to answer than others, as my previous posts can attest.  A couple of weeks ago, someone* inquired about a reference notation in the Internal Revenue Code of 1939, Public Law 76-1, 53 Stat. 1.  At the end of Section 22 on page 9, there is a notation that says, “98907°–39–PT. I–2,” as you can see in the image below.  The notation is periodically repeated throughout the volume, but the last number increases by one digit each time.

Notation "98907°--39--PT. I--2" in the lower left

I didn’t know the answer off the top of my head, though I assumed it was some sort of symbol to do with printing or binding.  After consulting around to my fellow law librarians who thought the same thing, but couldn’t be certain, I called the Center for Legislative Archives at the National Archives.  I ended up speaking to Rodney Ross, a reference librarian, who consulted Maryellen Trautman, another reference librarian, who used to work with government documents.**  Maryellen quickly provided the information that the symbols were the instructions of the printer to the binder to ensure that proper collation takes place (given that sheets are printed with four images per page and then folded and cut correctly).  The symbol is technically a signature, which in printing means:

a. A letter, number, or symbol placed at the bottom of the first page on each sheet of printed pages of a book as a guide to the proper sequence of the sheets in binding;

b. A large sheet printed with four or a multiple of four pages that when folded becomes a section of the book.

Ultimately, learning new and random facts like this is one of my favorite things about answering “Ask A Librarian” questions.  Even though this one, sadly, did not lead to a hidden treasure map.***

*The requester has kindly agreed to let me this share the information.

**Both reference librarians have kindly agreed to let me highlight their knowledge and how quickly they helped me answer this question.

***A public notice to my two brothers so they’ll know at least I’m looking.