The Signifyin' Monkey
Way down in the jungle deep,
The bad ass lion stepped on the signifyin monkey's feet.
The monkey said, "Muthafucka, can't you see?
Why, you standin on my goddamn feet!"
In a more general sense, if someone is said to be "signifyin"", it may mean that they are taking themselves to seriously by holding forth on deep portentious subjects in a self-important manner.
One might be describing pretentious intellectualizing or over-bearing preaching about matters which should make us humble by their mystery.
On which a passing co-worker commented, "There he goes signifyin' again."
Since I happen to be Jewish, I know exactly what he meant.