Here are a couple examples, and why we aren't using them.
"Summer sermons will be shorter. Priests play golf too." I can't help but rephrasing this ad as, "Our preaching is such a waste of your time that in the summer, when your leisure time is more valuable, we'll waste less of it." If our preaching isn't helping people live out their Christian lives in important ways, then we shouldn't be preaching. If it is, let's advertise that: "Hear a message that will change your life before your Sunday morning tee time."
"Why not surprise us and show up this Sunday?" When I showed this one to my deacon, he couldn't believe it. "We pray daily for those who need a relationship with Christ to come to us," he said. "We're expecting them when they come, we're not surprised." Really, would anyone want to go to a church, or anywhere else, that would be surprised and unprepared for their arrival? Many people don't return to a church they visit for precisely that reason. When we hung the banner off the side of our church last year, we included our purpose statement (Worship God, Care for People, Grow as Christians) with the message "We're Expecting You" underneath.
Then we come to "Come see what goes on between Easter and Christmas."
Then we have a couple of billboard suggestions directing people to twitter and Facebook. I can't see a billboard ad to drive people to Facebook or twitter. I think social media advertising is a much more helpful way to drive people to our social media sites and, if we are buying a billboard, let's have it share something more positive about us than "we are on Facebook and twitter."
For better billboard and advertising campaign ideas, I'd direct you to the Diocese of Ohio. Their billboards included the message: "Love God. Love Your Neighbor. Change the World." A church with that bumpersticker is one I'd be interested in trying, and so might my unchurched friends.