There are a few characters representing the concept of "happy" in the Chinese language. Each one is slightly different to be placed in context with what one is speaking about.
For instance, the "happy" that is used often with holidays, lei, bears resemblance to many drums marching down the street. "Happiness" is also a matter of the heart and you will sometimes see a symbol of the heart, detailed to the right here, as part of the character.The most well known symbol for "happiness" in Chinese is often referred to as the "double happiness". To begin with, the single symbol for happiness is the character xi.
If one could imagine looking at someone from above who is doing the infamous Snoopy dance and beating a drum that would be the image of this character. At the bottom is the symbol of mouth, open and wide ready to shout for joy. At the top is the symbol of drums, beating out our joy and happiness. Thinking about this image, it often reminds me of the simple pleasure a little child has just beating on pots and pans.
Taking those images to heart, that is the type of happiness this character is talking about. The symmetry of the symbol makes it "appealing" to the eye, a feature in Chinese writing that is just as important as the word itself.
When this symbol is doubled, we get the common character of shuang xi or "double happiness". This character is used during Chinese New Years as an emblem on signs, posters and red envelopes. Because of the "double" nature, symbolizing two, it is very common to be part of wedding or anniversary gifts.
