Freeway Overpass Signs

I don't know if this happens in other parts of the country but I've noticed an increasing number of signs being hung on freeway overpasses. You know, you're driving down the 118, look up and there's a bedsheet hung to the overpass that says "Happy 18th birthday, Natasha!"

Consider this, the average person is doing 55-65mph on a freeway and they have maybe 3-4 seconds to see your bedsheet that you spray painted on. This message is for one person (if they even see it) and it's a distraction to a thousand others.

The other thing that annoys me about this is it never gets taken down later that day - it sits there for 2-3 days until it falls off or the weather beats it down, which in my opinion, means it's on par with graffiti and/or littering.

Stop it already!!!