Most Renaissance depictions of the Son of God show him doing weird things with his fingers. I’m wondering if there is some iconic code that goes along with that, which might be decipherable.
Yes. It's called "the Da Vinci Code."
(ducking)
This might help:
I believe that the three fingers together in the gesture represent the Holy Trinity, while the other two fingers together are meant to show the duality Christ’s divine and human natures. Could be wrong but this is what I learned in Art History class.