San Francisco Muni begins to enforce imaginary no-photos policy

The blogger at What I'm Seeing is a prolific photographer of San Francisco's rapid transit system, and thus has fallen afoul of its imaginary no-photos policy, with a threatened arrest:

Before I could get the 1st shot off, Fare Inspector #32 started marching towards me, hands in the air, yelling at me to "STOP TAKING PICTURES!!" So I put away camera, walked towards him and answered his statement with a question. I asked him if he could site me the specific Muni code that prohibited a Translink Card carrying passenger from taking pictures of Muni Personal on Muni Property. He could not. Instead he responded that I "needed his permission" and demanded to see my "credentials" and the pictures on my camera. He added that in fact, if I was unwilling to turn over possession of my camera to him he would seize my camera and have me arrested.

What Is Muni's Photography Policy??

(Thanks, Ted!)