I lived and worked in the CA bay area for years and have watched that symbol “ = “ go from “ silence = death” to it’s current shortened form. I think it originally had something to to with the AIDS situation.
The sad irony is that it was true that silence equalled death, only it was the silence imposed by homosexual activists on anyone who tried to speak the truth, that it was the actual ACT of male homosexual sex that caused the transmission of the disease.
And silence DID equal death when the Red Cross didn't reveal to people receiving blood donated by active homosexuals that it contained the AIDS virus, endangering the lives of hemophiliacs like Ryan White and folks in hospitals receiving what they thought was life saving blood transfusions, but received a death sentence, instead.
It wasn't for many years after people became aware of AIDS that the problem of transmission though needle re-use became an issue. It started with homosexuals, and spread to the drug users.