The Pink Sheets were a printed list of over-the-counter stocks that were published by the National Quotation Bureau from 1913 until 1999, when the list went electronic. At that time, any stock that was not listed on an exchange was considered over-the-counter. 
They were called the Pink Sheets because the pink color of the paper that the quote were printed on. (There was a separate set of sheets for bonds called the Yellow Sheets.)
The Pink Sheets measured 5.5 inches wide by 14 inches long, and had 100 to 200 pages stapled at the top.
The columns on the list showed:
- The name of the company
- The stock symbol if any (yes, back in those days, many stocks didn’t have stock ticker symbols)
- The list of market makers in the stock (brokerage firms that would agree to buy and sell the stock to offer liquidity)
- The phone numbers of the market makers
- The bid price
- The asked price
In 1986, as an example, there were 328 pages (164 pieces of paper), and about 7,200 different stocks.