In 1984 I was in the US Army stationed in Germany. The day after the election I found the following written in the latrine stall:
Here’s to four more years
That was pretty gutsy for an Army guy to post in the barracks. Nobody was supposed to bad mouth Reagan.
Smoots is the ultimate in graffiti as far as I’m concerned.
I used to live in a town called Ontario. That name was on a water tower in the center of town. Someone changed it to Blow Farto. It was that way for years. One night I was riding arouind with friends, and someone mentioned it. For the first time, it was funny.
Can’t view the FB links. 
I think you have to make the photo public for non friends to view them…
I didn’t see it in person, but I quite enjoyed “GENTRIFY THIS!” complete with a giant cock and balls, spray painted on a hoarding in a rundown part of town.
Pic: http://www.artschoolvets.com/news/tag/platoon-culture-talk-graffiti-gentrification/
Church sign in my neighborhood:
God is the meaning of happiness. Now and forever.
As an Andrew Lloyd Webber fan, it cracked me up.
Why?
There is a charming story in Sydney of an old alcoholic, illiterate sailor who one day passed a seaman’s mission, heard the music and the sermon, and was suddenly struck with the capacity to write one word - Eternity.
He then made it his mission for several decades from the 1940s to the 1960s to go out at night and write the word “Eternity” - the name of God - using chalk and a distinctive laborious copperplate handwriting style, on walls and footpaths all around Sydney on as many surfaces as he could.
For years, people noted the words, but it was a complete mystery who was doing this until Arthur Stace was identified as the author in the 1960s. It is estimated that he wrote the word something like half a million times.
People became quite fond of discovering the quirky presence of the word as they moved around the city. That is why, in the fireworks display in Sydney for the turn of the millennium in 2000 (yes, I know-let it go) the centrepiece of the display was the word written in Stace’s distinctive style in fireworks on Sydney Harbour Bridge.
The Florence water tower always attracts attention.
Once I saw a sticker, a cat caricature, with a little mustache and right arm sticking up, under it “Heil Kitty”
Hey, I’ve driven past that several times. Now I feel like I missed out by not stopping at the mall, or joining in on the Labor Day festivities. Yes, my life is that dull.
Winding roads in Australia sometimes have a sign reading ‘Do not overtake unless safe’. I like the idea that elsewhere, you can overtake whether it’s safe or not.
You may have seen this sign. In Oregon there are two towns called Oregon City and Boring. Which leads to this actual exit sign from Hwy 212:
I’ve seen that sign many times. It never occurred to me that some people would find that combo amusing. To me it just means I’m almost home. 
I’m very fond of this one, which I’ve seen in numerous places:
http://wordsallaround.blogspot.com.au/2009/11/great-use-of-two-letters-of-alphabet-to.html
A new one in our neighborhood culvert.
" Bill Cosby "
Who knows…maybe the real Bill Cosby actually does get his kicks late at night with a can of spray paint thinking “those fools will never think it actually WAS me and the joke will be on them bwwwwaaahaaahaaa”
I thought of this thread this afternoon when I drove past a sign outside a local pub advertising an “Evening of Clairvoyance”. The temptation to print out and paste onto it a banner reading “Cancelled due to unforeseen circumstances” is almost irresistible.
Do it! Do it! Do it!
And take a picture and post it!
I like the story of the guy who defaced the poster for The Usual Suspects with “Keyser Söze”, and an arrow to the location of the appropriate cast member.
Not a sign per se, but I saw a license plate last week that was “BLU BYU”.
I wasn’t sure if the owner of the vehicle was attesting to his speeding or his relations with the co-ed population of a certain institution of higher learning in Salt Lake City.