Yes, it’s from the same church sign that gives us the “join our Kids Krusade” every year (there’s an old thread on it).
Now the sign says “Church isn’t where you go, it’s what you are.”
I could grok it if it said “it’s what you do” or “it’s who you are”. All implying that the church is not a building, but the people who are members in it.
But that particular use of the word “what” has thrown me a bit.
Does my interpretation still hold? Perhaps I’m just being (characteristically) dense.
Your opinions.
I would say your interpretation still holds. Since the New Testament teaches that all christians are the bride of Christ and are his church then the church would be ‘what you are.’ I wouldn’t call you dense…but since you said it first… 
I take it to be a reminder that the literal meaning of church is more along the lines of “the group of believers” or the followers of Christ.
It’s actually a good message for those that think that 1 hr on Sunday means that they can act like a-holes the rest of the week. If you are a follower of Christ, you are always in church.
Sounds to me like an awkwardly worded reminder that the church is not a building, the church is a people.
And has managed to get "I am the church " stuck in my head–although, in fairness, singing it in church yesterday might have something to do with it.
To me, it sounds like the “what” emphasizes the Church more than the individual.
ETA: And by Church, I meant the group of people, as Eureka said.
OK, I got it then, I’m just being denser than usual this week.
Thanks.
I figure that old children’s finger rhyme makes more sense if you run it backwards.
"Here’s the church (fingertips up & wiggling) with all its people,
Here’s the building, and here’s the steeple (fingertips folded inside, index fingers form steeple.)