There is almost always a cop there. I walk by pretty frequently and I can't recall seeing it open without a cop. Could be wrong - not exactly casing the joint on my lunch walks.
It would only be a protection racket if the cops were conspiring with those who commit the robberies. Lots of businesses pay for security for all kinds of obvious reasons; just because the cost of security is deemed to be lower than the cost of not having it doesn't mean that anyone is running a "racket".
But the DA and police chief choose not to pursue property crimes or even assaults... the officers themselves are probably not conspiring, but it's a culture of "leave the criminals be" which leads to needing this extra protection, and it's all coming from the same organization.
They are among several SF businesses that hire off-duty cops under a program called “10-B”. They pay the officer’s overtime wage ($100/hr) plus a 14.7% admin fee to the city. Details here: https://www.sfchronicle.com/bayarea/philmatier/article/Busin...
Serious question: Are the off-duty police allowed to do anything if a "small" crime happens? Or is this for security theatre only?
I mean, if I steal a 4TB SSD, it's unlikely there's going to be a prosecution right? So are they going to risk the career damage of brutalizing me when I resist, or knocking out some teeth tackling me if I decide to run?