How about a sign that says “The natural world is only that which can be measured. How much does love weigh? How tall is humor?”
Alternatively, I’d put up a poster quoting Romans 1:18-23., with verse 22 in bold.
That’s my favorite argument against atheism — the mind. The fact that our thoughts and perceptions can’t be measured yet still exist blows a hole in atheism’s materialist premises big enough to drive a Mack truck through.
“they...became vain in their imaginations, and their foolish heart was darkened.
22Professing themselves to be wise, they became fools,”
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Merry Christmas!