福（fú） is the Chinese word for blessing and happiness. Looking at the oldest known script, 福 originally depicted two hands holding a jar in front of an altar, symbolizing someone asking for blessings from gods via sacrificial offerings. Whether in the form of happiness or blessings, if you were in divine favor, you could be sure that deities would give you 福.
Prior to the New Year, many Chinese will attach a 福 sign to their doors to invoke blessings for the coming year. This rite originates from an old tale:
Once upon a time, there was a beast that loved to eat children. In fear of this beast, people put a picture of a goddess on their front doors. Scared by so many deities, the beast, in the end, disappeared. This picture of the goddess was simplified over the years, and eventually became the 福 sign. But if you are very observant, you might notice that the 福 sign is often attached upside-down. Why? In Chinese the symbols for “turning something upside-down” and “arriving” have the same sound—dào. So an inverted 福 sign conveys the meaning that happiness has arrived.