In India, skulls played a particularly important role in religious depictions. Skulls often adorned ancient gods and goddess as necklaces or bracelets, showing their ability to conquer death.
Life and death are both part of the cosmic drama and are embraced- not resisted.
Buddhism and Tibetan Buddhism take it a little deeper, instead of representing death or loss, it represents the important Buddhist concept of emptiness. In Buddhism, emptiness is considered to be a quality of the universe.