Not only is it confusing, there’s something else wrong with it. (Hint: Look at the upper right.) That aside, this isn’t the worst of DC’s reversible-lane signs; I’d pick the entry ramp signs to Rock Creek Parkway, which have a giant DO NOT ENTER and then, in small type, something like “6:30-9:30 am weekdays”. It always makes me stop for a split second (usually in the middle of the intersection as I’m turning across traffic to get on at P Street), and if I have a passenger, they invariably yell, “wait, it says do not enter!”
I also immediately recognized the city where the sign on the left below appears, as I’ve driven through intersections like that (probably that very one) many times. The meaning of the right-hand picture, though, had me stumped.
I shared Jalopnik’s initial reaction: “look up to see how many planes are landing or taking off before attempting a left.” It’s always a good idea. (Here‘s the real, but still not entirely sensible, answer.)