As a Westerner these can be somewhat disturbing and I have hesitated to share this part of their culture. It symbolizes the tip of a penis inside the vulva of a woman. We saw them in both Bhutan and Nepal. Probably best if I let Wikipedia do the explanation.
In Hinduism, Shiva is symbolized and worshiped in a form called Lingam, which shows his phallus merged with vulva of Shakti, his consort. Lingam is the most powerful fertility symbol in Hinduism, showing the critical union of Shiva and Shakti. Shiva is depicted with River Ganges and moon on his head.
This image was one of about 10 small structures exactly like this one at the funeral temple. But keep in mind that they believe that in birth, another has been reincarinated, so both conception and death are to be celebrated.