That's not a Nanner, its a full on pollen sack. Sometimes MJ will be asexual, and grow fully developed male and female flowers.

Hermi flowers will develop a single pistle and a pollen gland in the same flower, the single pollen gland is the dreaded "Nanner" it's not as much a risk of seeds tho since most of the time the pollen is inactive.

Another sign of potential hermi I've seen is multiple pistles sticking out of a single calax.

Pic 1: Nanner
Pic 2: Female flower with 6 pistles off of same plant.