Mooncakes
If you are in Hong Kong during the Mid-Autumn Festival, it will be impossible not to notice mooncakes. They are believed to have originated from Yuan dynasty (1271-1368) revolutionaries, who are said to have used the pastries to pass secret messages between each other.
Source: http://www.discoverhongkong.com/eng/see-do/events-festivals/chinese-festivals/mid-autumn-festival.jsp#ixzz3KMoc3o8k