San Diego/Orange County

 "Silence is the ultimate weapon of power."

 - Charles de Gaulle

 First Amendment Protected signs placed along Interstates 5, 15 and 405 in Orange and San Diego Counties.

Above is next to southbound 5 and only visible to northbound traffic. Removal requires a 20+ mile detour some 75,000 cars per day probably won't be making.

Whenever driving, look for spots like this on divided highways with few exits.

Posting Method: rocks on cardboard flap.

Posting Time: approximately 7 seconds.

 El Toro Rd, Irvine CA. Requires a 50' walk from quiet cul-de-sac parking, generally up for days at 160,000+ cars per day.

 If you want to play the game, you have to Make The Signs.

With a commanding view of southbound 5 and invisible to northbound, this fence tucked behind bushes in a quiet corner of the San Onofre 5 north rest stop is a classic can't-get-there-from-here posting spot. Even though it's only 500 feet from its audience, it's gonna cost you about 30 miles if you want to take it down. Beautiful drive though...

 Sign above is another easy-to-see/impossible-to-reach masterpiece. Ultra-high visibility to both south and northbound 5 at just north of the 78 interchange. The only exit that’ll get to it is Cassidy St., which is southbound only and happens before you can see the sign. If you’re northbound you have to turn around three miles ahead, double back to Cassidy, take down the sign and then… well, you’ll make it back eventually. But historically, some 200,000 of you a day (minus night,) aren’t going to do that for a few days at least.

Signs above and below are on I-15 in San Diego. 
Posting method: Slide Cardboard between rails and fencing. 
Posting time: approximately 11 seconds.
Duration: Two days last I checked.

Signs Posted since 2003 - 7,664
Arrests - 0

Southern California

"Lying is done with words and also with silence." - Adrienne Rich

First Amendment protected signs placed on freeways around southern California. 

"In a day when you don't come across any problems — you can be sure that you are traveling in the wrong path."

 -Swami Vivekananda

"Do what you can, with what you have, where you are." -Theodore Roosevelt

 "One of the definitions of sanity is the ability to tell real from unreal. Soon we'll need a new definition." - Alvin Toffler

"There is nothing more dangerous than the conscience of a bigot." - George Bernard Shaw

 "Not everything that is faced can be changed. But nothing can be changed until it is faced."

—  James Baldwin

 "Things do not happen. Things are made to happen." - John F. Kennedy

Signs Posted since 2003 - 7,653

Arrests - 0

SF Bay Area

"Activism is the rent I pay for living on the planet." - Alice Walker

 Signs placed over and alongside freeways in the San Francisco Bay Area.

 “You know, a long time ago being crazy meant something. Nowadays everybody's crazy.” - Charles Manson

 "Possession isn't nine-tenths of the law. It's nine-tenths of the problem." - John Lennon

 “In the End, we will remember not the words of our enemies, but the silence of our friends.” - Martin Luther King Jr.

 “I never forget a face, but in your case I'll be glad to make an exception.” - Groucho Marx

 “Life begins at the end of your comfort zone.” - Neil Walsch 

Signs Posted - 7,637
Arrests - 0

1st Amendment Protected Signs in San Francisco

"Don't hate the media. Become the media."

 - Jello Biafra

 Signs placed by freeways in San Francisco

Quotes by San Franciscans.

 "The only people for me are the mad ones, the ones who are mad to live, mad to talk, mad to be saved..." - Jack Kerouac

 "If a bullet should enter my brain, let that bullet destroy every closet door in the country." - Harvey Milk

  "Somebody has to do something, and it's just incredibly pathetic that it has to be us." - Jerry Garcia

"I think the reason Jesus is so popular, just on a celebrity level, is that he died at the peak of his career.” - Marc Maron

"No matter what people tell you, words and ideas can change the world." -Robin Williams

Signs Posted -  7,626
Arrests - 0

Signs on Los Angeles Freeway Overpasses

 “Can’t let the government tell me 

how my future lookin’.”

 – Kendrick Lamar

 First Amendment protected signs placed on Los Angeles freeway overpasses. Quotes by Angelenos.

 “The propagandist's purpose is to make one set of people forget that certain other sets of people are human.” - Aldous Huxley

 “What did it matter where you lay once you were dead? In a dirty sump or in a marble tower on top of a high hill? You were dead, you were sleeping the big sleep, you were not bothered by things like that.” - Raymond Chandler

 “If the world should blow itself up, the last audible voice would that of an expert saying it couldn’t be done.” - Peter Ustinov

 “It’s important for all Americans to know how vulnerable our Constitution is.” - George Takei

 "There's something just as inevitable as death. And that's life. Think of the power of the universe — turning the Earth, growing the trees. That's the same power within you — if you'll only have the courage and the will to use it." - Charlie Chaplin 

 “Blame is for God and small children.” - Dustin Hoffman

 "Things are never so bad they can't be made worse." -Humphrey Bogart

Signs Posted - 7,617
Arrests - 0