Well, I don’t think he was just scribbling. It’s too convincing.
Unlikely that it is a vector-graphics equation for the lines and filled areas that constitute the smiley face. Right?
But if mostly a blur-retrace of something real, then what in particular? An elaboration or derivation of part of Maxwell? [Though that would work better for the “Let There Be Light” referenced in the GoComics comments.] Something from General Relativity? Thermodynamics? We are happy because the Sun keeps shining?