They're seriously distorting the quote they use. We don't know the name of that group, though. We will, no doubt, but it's not up there on the billboard.
Will most Christians reject what that billboard represents? I don't know, actually. Many won't even understand the reference it makes, or will misinterpret it in some way. That use of "Word" is exclusive to the Bible, and to some English translations. It's understood differently by different groups of Christians.
Which supports the point I was making. We don't know how "Christians" feel about that billboard, nor are we likely to know. Those who disagree with what it represents will probably not say anything publicly about their disagreement. Those who don't understand the billboard will also remain silent.
All Christian denominations self-identify as Christian. But that can mean a lot of different things. The term "Christian" is really meaningless, except that it has something to do with some guy who may or may not have lived a couple thousand years ago. Beyond that, every denomination interprets it all differently. And individual members of those denominations have their own interpretations.
There is little in common, really, for all Christians. Just some guy named Jesus (not actually what he was called at the time) and some mixed-up stories about what and who that guy was.
When we use the word "Christian" to describe someone or some organization, the meaning of the word is very, very foggy. It means something different to everyone. Again, my point.