Now that we have moved the bench, the bricks too have been cleaned and re-laid in the new spot. I remembered about the city hall story, and started looking for more info online as the link in my 2009 post had expired. And lo, I found an article about these very bricks.
Years Brick Made: 1870s
Type: Red common duty
Comments: Bricks were made specially for the San Francisco City Hall, San Francisco, CA. Numerous brick manufacturers from San Francisco, San Rafael, San Jose, and Sacramento provided the bricks and stamped the bricks with CH, which stands for City Hall. This is unusual because most bricks are usually stamped with the maker's name, not its destination. However, the variations in these bricks demonstrate that they are not from a single maker when comparing them side by side. Local brick manufacturers who supplied the City Hall with brick as gathered from the records of San Francisco included G. Oliva, P.N. Carroll, D.S. McDonald, Clauss Witt, Theodore W. Peterson, G.D. Nagle, Thomas D. Tobin, Merrill & Black, Remillard Bros., Patent Brick Co., Diamond Brick Co., Hunter & Shackleford, E. Wilson & Co., William Sharon, J.S. Bellrude, Eli Bonnet, Philip Caduc, Michael J. Kelly, Thomas Boyle, and John Tuttle. Note that none of the maker's initials match C.H., which verifies the 1884 report written by State Geologist Henry Hanks, who wrote:
"The initials C.H. impressed in the brick of which our new City Hall is built, put there to denote that they were intended for that edifice, may (should they prove to possess the lasting properties claimed for them) become to the antiquary of the remote future a source of much worriment as he labors to decipher their probable meaning."
Source: Museum of the City of San Francisco, Cannery Shopping center, San Francisco; San Francisco Municipal Reports, 1871-1881; Hanks, 4th Report of the State Mineralogist, 1884, p. 144.