Effete Snob has already posted the classic image. Here's an article about graffiti on the B&O bridge over the years.
Mon Dec 29, 2014:
It's no "Surrender Dorothy."
First, this is not a safe practice. CSX doesn't want you out on its bridge, especially in the dark, spray painting. Second, if you fall, you're in big trouble. That said:
Go Home Already: In On The Graffiti Tagger

Some context...
Surrender Dorothy
It's in the Washington Post this morning:
Fugazi, a standout from D.C.s musical past, pops up in an unexpected place

Someone has painted "Fugazi" -- a famed Washington post-hardcore punk band -- on a railroad overpass over the Beltway in Kensington, Md., seen on Sunday. (John Kelly/The Washington Post)
Here's the reference:
Surrender Dorothy painted on a Beltway overpass whats the story?

A 1986 photo shows the Beltway overpass, close by the glistening spires of the Mormon Temple in Kensington, with the graffito. (United Press International)
The adjacent footbridge gets tagged too:
D.C. Temple graffiti prank won't die
Compiled by Michael De Groote, Deseret News
Published: Tuesday, July 26 2011 1:55 p.m. MDT
@degroote or @DeGroote
mdegroote@desnews.com
degroote
WASHINGTON D.C. Who did it?
Who played the part of the Wicked Witch of the West and was the first in the early 1970s to spray paint the message "Surrender Dorothy" on an overpass on the Washington D.C. Beltway right where the Mormon Temple comes into view? The mystery is now, at least partially, solved.
Christine Mulligan of Germantown, Md., wrote to "Answer Man" John Kelly at
The Washington Post last month to see if he knew the orgin of the painted prank.
He didn't at first.
{snip}
Several people
responded to The Washington Post's Answer Man's request for information.
{snip}