This is a mask of the common Hindu deity Hariharan, half Lord Hari (Vishnu - pictured on the left side of the image) and half Lord Hara (Shiva - pictured on the right side of the image in white.  Together they represent the basic unity, not only of Lord Vishnu and Lord Shiva, but of the basic unity of all the Gods, as well as the unity of humankind and all creation.  One represents divine maintenance while the other represent divine destruction.
     Both halves of the mask sport half of the sectarian Vaishnava (vertical double line) and Saiva (three horizontal lines) on their respective foreheads.  Additionally the skin coloring of the left side, representing Lord Vishnu is appropriately blue in color, while the depiction of Lord Shiva on the right is appropriately white (although he is commonly shown as blue in some pictures, his true color is the white of sacred ash).  They are both parts of the Hindu Trimurti, or trinity, made up of Brahma, Vishnu and Shiva (or just as validly of Devi, Vishnu and Shiva) and accompanied by their powers (consorts) Saraswati, Laxmi and Parvati (all aspects of creation and the Divine Feminine).