Why are all the landmark buildings in San Francisco lit up with red lights?

Might have something to do with the 49'ers. Football season is starting up again.

To stop things flying into them?

If it's "recent" -- then it's probably 49'ers colors. If it's the same color they've always been, then it's the low pressure sodium vapor lights-- and so sort of yellow-ish.

(And yes, they all have blinking red lights ontop of them, Gavel)

I know that they did lights at city hall when barry bonds won the world record for home runs. I think that’s probably why the rest did too.