When Data was stranded in 1893 after an accident caused by the Unnamed Devidians on Devidia II in 2368, he found out which year he had been transported to by means of an old front page of the San Francisco Register he found on the ground. The page was dated 13 August 1893, Sunday, and also mentioned a recent Cholera outbreak, from which hundreds have died. The page also mentioned that the San Francisco Register is the leading newspaper of the Pacific Coast.
Later Data found a picture of Guinan in a page of the San Francisco register, which was handled him by Jack London, who wrapped a croissant in it. Guinan's picture was above the headline "Literary Reception announced" and the page was dated as Friday, 11 August 1893. (TNG: "Time's Arrow")
When the bridgecrew of the USS Enterprise was in the San Francisco of 1986, they encountered a box where the Register was sold, which made the crew aware about the necessity of money.
In that year, the tag line for the newspaper is Largest Circulation in the West, and the phone number for the Register is 555-7722 and each edition cost 25 cents. (Star Trek IV: The Voyage Home)
The "San Francisco Register" is actually a fictional newspaper; it has made appearances in a number of television series, including "Journeyman", which places its offices on Market Street.