Thanks to my friend Ann, I just found a web site devoted to the Lepcha language:
The Lepcha language is spoken in Sikkim and Darjeeling district in West Bengal of India, in the Ilam disctrict of Nepal and in a small enclave in south-western Bhutan, altogether probably by upwards of 50,000 people. Lepcha is unmistakably a member of the Tibeto-Burman language group, but its exact position within the language group is still an open question. Lepcha is considered to be one of the aboriginal languages of the area in which it is spoken. Unlike most other tribal languages of the Himalayas, the Lepcha people have their own indigenous script.
Here is a sample of what that script looks like:
According to Lepcha tradition, the Lepcha script was invented by the Lepcha scholar Thikúng Men Salóng, a contemporary of the patron saint of Sikkim, Lama Lhatsün Chenpo (also known as Lhatsün Namkha Jimi, 1597-1654).The invention of the written language is likely to have been motivated by the religious activities of Buddhist missionaries. The Lepcha literary tradition can be dated back to the eighteenth century, when the indigenous Lepcha script was devised during the reign of the third chögel of Sikkim, (imperabat 1700-1716).
UPDATE: This site has nice pictures of the script, as well as a map.