First thought that came to mind were the skull & bones of yale, stealing gerominos skull. Maybe its a persons skull from the lodge they represent.
THE MAHASIDDHA TRADITION IN TIBET by Vajranatha
The Higher Tantras could not be a congregational practice of monks because Tantric sadhana, as well as celebrations of the High Tantric feast or Ganachakrapuja, required partaking of meat, wine, and sexual intercourse. At the very least the latter two would force a monk to break his vows. And so what came about in the eleventh century was a change in the external style of practice; the Anuttara Tantras, many of them freshly brought from India and newly translated into Tibetan, came to be practiced in the style of the lower Yoga Tantras. Although there is a great deal of ritual in the Yoga Tantras, there is nothing there that would require a monk to violate his monastic vows. The presence of a woman or Dakini is require at High Tantric initiation and also at the Tantric feast of the Ganachakrapuja, but in the eleventh century reform the actual Dakini physically present was replaced by a mind-consort (yid kyi rig-ma), a visualization of the Dakini. One did the sexual practice only in visualization, not in actuality. In this way the practices of the Higher Tantras could be taken into the monasteries and incorporated into the congregations practice and liturgy of the monks known as puja. Unlike the Zen Buddhists of Japan, Tibetan monks customarily do not practice group meditation. That is something done in the privacy of one's room or in a retreat situation. The typical congregational practice of Tibetan monks is puja which may involve the chanting of liturgies and the making of offerings for many hours.
Partaking of a little wine or meat during Ganapuja is allright because in the course of the ritual they have been mystically transmuted into nectars, and the holy red and white substances in the skull cup have been replaced by symbolic substitutes.
But if one were to read the text of the liturgy, they are filled with the activities of wrathful deities which are both sexual and sanguine. But otherwise, everything is perfect monastic decorum. This was so successful a solution to the dilemma that all four schools of Tibetan Buddhism almost exclusively practice the Anuttara Tantras, to the neglect of the Yoga Tantras. Nonetheless, the Yoga Tantra transmissions have been preserved, especially in the Sakyapa school which is quite fastidious about preserving all of the authentic Indian Tantric transmissions. Among the Nyingmapas, who preserve the traditions coming from the early period of the spread of Buddhism in Tibet (7-9 cen. CE), practitioners of the Higher Tantras who do not take monastic ordination and become monks are known as Tantrikas or Ngagpas (sngags-pa), meaning "those who use mantras (sngags)". They are typically married Lamas. A Lama, though functioning as a priest and teacher, is not necessarily a monk.
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