In an early version of the script for Avengers: Endgame, it showed a lot of cities with their own Wall of the Vanished so that you really get the sense of the scale of the impact from the Snap. Barring any contradictory evidence, I think we can assume every city still has these and they just weren't shown so this one would just be for the city and possibly its surrounding area.
And that theme of loss is continued when Scott Lang visits a memorial to the dead in San Francisco.
McFEELY We used to have beats in the script where there are those in every city. Millions of names.
MARKUS It’s that sense of collective trauma and the fact that if you weren’t killed, you wake up the next day — the trauma happened and I’m still here. How do we deal with this? That was the Stan Lee trick. Where’s the anxiety coming from? Now that they have Power X.
The New York Times, ‘Avengers: Endgame’: The Screenwriters Answer Every Question You Might Have
I don't think we really need to count the names on a stone, count the number of stones and estimate from there to come up with a rough figure. Instead we can use the rough population counts from our own world as there shouldn't be much of a difference. According to World Population Review the population of San Francisco in 2018, when Avengers: Infinity War took place, was 883,305 and the population of San Francisco-Oakland-Hayward, CA Metro Area was 4,729,484. As the Snap took out "half of all life" we can figure it would take out roughly 50% of all life from San Francisco and its surrounding area. Therefore, there would be roughly between 441,652 and 2,364,742 names in the Wall of the Vanished.