What is the significance of skull tattoo?

A guest in my family is Tibetan. He said the skeleton is Caparra in Tibetan.

Tibetan bone products are commonly known as kabbalah. Its materials are usually taken from the bones of women who died in childbirth and donated to temples by relatives of the deceased. Buddhists believe that a woman died in childbirth because her sins in her last life were too heavy. Donate her bones to make a vessel, and she can wash away the sins of her previous life so that she can be reincarnated as a good person in the next life.