I see a veritable plethora of billboards on my way to and from work every day, and the importance of proofing never escapes my thoughts. The most recent offender is a huge billboard for Lone Star Ford.
The billboard says "exit Shepard," which is unfortunate, because to get to Lone Star Ford, you really have to exit Shepherd. I can see a confused driver or two saying, "Was that the exit?"
Location-specific billboards with directions on them are a great way to drive people to a location, and can be very effective, even devoid of creativity. However, you have to make sure to point your potential customers in the right direction, because two letters can be the difference between ka-ching and "Was that our exit?"