"I refuse to prove that I exist," - Says God...
"...for proof denies faith and without faith I am nothing."
-HitchHikers Guide to the Galaxy.
This panel is a little questionable. The readers might not understand it.
For starters, you have God on a lie detector stating that he is lying.
Wouldn't it seem more plausible if God's lie-detector went on the fritz? Making it vague? Many might interpret it as a statement against Religion or that Atheism is absolute.
However, if you wish to keep this panel the way it is...you should make God really look like "God".
Draw his body glowing or something. That way, the reader goes..."OH, He IS God, but he can't prove that he exists."