The lion with Durga on it is the symbol of the Divine Consciousness acting through a divinised physical-vital and vital-emotional force. The lion is the attribute of the Goddess Durga, the conquering and protecting aspect of the Universal Mother. The Death's Head is the symbol of the Asura (the adversary of the gods) vanquished and killed by the Divine Power. page 389-90 , Letters on Yoga , volume 22 , SABCL