Let us be totally clear here: this post isn't intended to rag on either organization for bicycle locking ignorance. One organization is a government service tasked with crime prevention and security, the other parses vast amounts of information to provide us with the best resources available on any given subject, so it makes total sense that they'd be blanketing San Francisco with posters incorrectly telling people how to properly lock their bicycles. I mean, neither is a bike company, so how would they know?
Therefore, in the interest in preventing anyone who may have seen this from being duped into this subpar locking strategy, we'd like to remind everyone how to actually lock their bike (via Sheldon Brown):
People tend to buy the big clunky U-locks because they don't know how to use them properly. A U-lock should go around the rear rim and tire, somewhere inside the rear triangle of the frame. There is no need to loop it around the seat tube as well, because the wheel cannot be pulled through the rear triangle.
Some will object that felons might cut the rear rim and tire to remove the lock. Believe me, this just doesn't happen in the real world. It is indeed possible to cut the rim with a hacksaw, working from the outside to the inside, but first, the tire must be removed or cut through. It would be a lot of work to steal a frame without a usable rear wheel, the most expensive part of a bike, after the frame.
The main reason SFPD/Google's suggested strategy doesn't work is the same reason cable locks just plain don't secure bikes: every thief has a pair of cutters that make quick work of the cable. If you use their locking suggestion, not only are you carrying around a relatively useless, bulky cable, you're likely to find both your wheels stolen, as opposed to just your front wheel.
Google it if you don't believe me.
Update: Matt Friedman of SFPD tells us the SF Bike Coalition is behind the poster and locking recommendation. Yikes.