Last year I discovered an interesting tidbit about no-parking signs in Austin. When the city installs a new sign, they scratch the date of installation on the back of the sign.
This seemingly trivial fact helped me get several parking tickets dismissed.
I had found a legal parking space without a meter or sign across the street from my downtown loft. I parked my car there so that guests could use my reserved space in the parking garage. Since I mostly walk and ride the bus, I left my car parked on the street for a week or more.
One day I was walking home from the bank, and I noticed that there were several parking tickets on my windshield. I then noticed that they had installed a no-parking sign during the time my car had been parked there!
I went to court armed with a photograph of the back of the sign showing its date of installation, and the judge summarily dismissed the ticket.