Presented both for frank and helpful advice to those of you contemplating releasing videos of your public sex acts on mass transit, even in groovy ol' San Francisco, and to contemplate why public transit police don't have anything better to do with their time than to "investigate" a harmless stunt that already happened to no apparent harm to anyone or public order, this report from last week from CBS Local San Francisco:

Bay Area Rapid Transit police are investigating an amateur pornographic video apparently shot on a moving train.

Deputy Chief Ben Fairow said the cell phone video shows a "partially disrobed" couple having intercourse on a seat at the end of a BART train car.

The video was apparently filmed by a third party, and the man and woman in the video appear to know that someone is filming them. Fairow said the video does not show whether other riders are in the car.

The video quality is good enough that investigators are hopeful that they'll be able to identify the couple.

Fairow said lewd conduct on BART is a misdemeanor and can result in a system-wide banning.