Ah, the Ferry Building Stairs, or should I say the HISTORIC stairs? I like this sign. It's been there for quite some time and it never fails to make me smile.
I suppose someone felt that, by placing the adjective in front of stairs, incorrigible stair-sitters (and they are legion, I assure you) would be deterred because, well, the stairs are HISTORIC. The ferry building DOES suffer from a dearth of seating (if you're not eating at a restaurant). Perhaps they could install some non-historic benches.