How did these signs come to be hidden from public view? Accessible only to immediately adjacent neighbors and those with computer access?
Well, I’d wager that some of these signs were never meant to be viewed from the street. Between the hilly terrain and plethora of tall buildings in the Tenderloin, a sign could be targeted at the view of an adjacent high-value hotel or apartment with little concern for street traffic. Think of it as a proto-targeted ad campaign.
Also, I’d additionally wager that some of these hidden signs are the end result of post-1906 earthquake construction. Leveled by quake and fire, the Tenderloin was reconstructed in fits and starts from 1906 to 1912ish (and in some cases much, much later). Hence a sign that was visible to street traffic in 1907 might have been obscured by new construction as early as 1908 or 1909.
For example: 572 O’ Farrell Street – which contains a MJB Coffee sign on it’s Geary-facing side – was constructed immediately post-quake in 1907. While I’m not sure of the sign’s vintage, I do know the sight lines to Geary weren’t blocked until the construction of 669 Geary in 1922. That means it’s possible the sign enjoyed 15 years worth of high impact visibility – that’s more than enough time to pay off the salaries of the walldogs who painted it.