Ideas:

1. Instead of the usual gesture for a sitting person seen sideways, that is with hand towards mouth, probably meaning 'eating' (in the wide sense, i.e. kai), we have here the uplifted arm ending in a kind of fork.

I believe we should see this as a sign meaning 'support', here perhaps corresponding to offerings to the gods. They need support of various kinds, being similar to human chiefs.

2. The limbs of the human body are similar to the limbs of a tree. To support the roof of a house you can use upright logs ending in Y, and into these forks horizontal beams may then be placed.