A few hours ago, a local group paid for eleven different signs to go up about Cleveland and Akron [click]. Supra, is #1. They are calling this their "Out of the Closet Campaign".
It is a personal thing, whether one believes in a God or does not. Some can, some would like to, some can not. Those in the middle suffer a sort of anguish, a desire for a presence that seems absence. Perhaps, one day they can find peace one way or another.
Whether one is a theist or an atheist, either can be good or not as a human being. There are good and bad people, within and without. All men are brothers. In search for peace in the world, it is important to have good will. Most religions proclaim the good. One does not have to have religion to also proclaim, and do the good.
One unfortunate thing about some atheists is that they promote unpleasant exemplars (Madalyn Murray O'Hair, Richard Dawkins, Christopher Hitchens, Ayn Rand). These are shitty heroes. They prefer confrontation, to gain some selfish sense of superiority. This sort of (often strident) mean-spiritness prejudices many against atheists.
These billboards attempt to be positive about unbelief. Perhaps, it is a plea to enter general society as an equal member.