If God wants to send me a message, I sincerely doubt he'll choose a billboard as the method.

As long as the billboard company is willing to give (sell) equal space to opposing views, I'm indifferent to it.

Over the course of a long and very corrupt life, I've come to understand a thing or two about my religious beliefs. For example, I've concluded that God speaks to us and helps us through each other. No concrete evidence, just an observation that whenever I've needed help it has come, and through another person.

Whether you agree with the message or not, the medium does not invalidate it.