The Lisu people are mostly living in west Yunnan as well as valleys and hillsides along the Nujiang River, Lancang River and Jinsha River in the northwest of the province. The ethnic group is classified into White Lisu, Black Lisu and Colored Lisu according to the different colors of their gunny clothes. Men and women of the ethnic group usually resort to the traditional means - singing songs - to foster their affections when falling in love with each other.
In order to avoid disturbance from others, the Lisu lovers would sometimes contact each other in such ways as playing lute/mouth string, blowing/scattering tree leaves, tying grass blotches, etc., so as to confirm the time and place for their secrete date.
Source:
http://traditions.cultural-china.com/en/115Traditions3872.html
