This symbol stands for the most complex initiation system known in Tibetan Buddhism. The Dalai Lama has given many Kalachakra initiations across the world.
Kalachakra means literally "Wheel of time". The Kalachakra Tantra also mentions Shambala, which is hidden kingdom in Tibetan Buddhism. The Tantric initiation is meant to ensure the practioner's rebirth in this paradisiac Pure Land.
This symbol is frequently seen in Tibet, for example on doors and in temples. It is esoteric symbol representing the Kalachakra Tantra initiation.
The moon and sun at the top represents the union of opposites, of method and wisdom, the key to enlightment.
The Kalachakra mantra consists of ten syllables that represent, among other things, the four elements of air, fire, earth, water.
Nada / Tila
The nada or tilaka refers to the mind mandala
Disc
The white disc refers to the body mandala
Crescent
The crescent refers to the speech mandala
HAM
The symbol for 'HAM' refers to the Enlightened Wisdom of the mandala Deitiea
KSHA
The symbol for 'KSHA' refers to the Body, Speech and Mind of the Deities
MA
The symbol for 'MA' refers to the Mandala Palace, with its four different colors in the four main directions
LA
The symbol for 'LA' refers to the yellow Earth circle around the mandala palace
WA
The symbol for 'WA' refers to the white Water circle around the mandala palace
RA
The symbol for 'RA' refers to the red Fire circle around the mandala palace
YA
The symbol for 'YA' refers to the black Wind circle around the mandala palace
E
The symbol for 'E' refers to Kalachakra [Method]
VAM
The symbol for 'VAM' refers to Vishvamata [Wisdom]
Ring
The Protective Fire Ring represents the outermost Wisdom circle around the mandala