Chinese character is one of the most interesting written languages in the world, as it composed with different kind of classifications like pictograms, simple indicatives and compound indicatives etc. Among all, a Chinese word "Hei" ("囍" in Traditional Chinese or "Xi" in Mandarin) which you can always see it in Chinese celebration events. It is a symbol which has the meaning of joyful, bliss and auspicious to the new married couple.
There's a meaningful story behind the "Hei". The famous Chinese poem writer - Wang Anshi in Song Dynasty, he designed "Hei" from his life experience. When Wang was young, in his way to the imperial examination, he saw a couplet outside a renowned family called Ma. However, he was hurry for the examination, so he didn't complete it. During the imperial examination he found that this couplet was in his examination and he was delighted. After the examination, Wang visited the Ma's family to complete the couplet. Ma was happy to his answer and so Wang got married with Ma's daughter. On the wedding day, Wang received the good news from imperial examination. As Wang was getting married (one happiness) and received the good news from imperial examination (another happiness), he designed to put the "喜" (means happiness) to become "囍" (means double happiness). Thus people keep using it in weddings as a pair of happiness means fortune to the couple.
Many people love this and it will be great if you can put on something about "囍" in your special events like a wedding party! Some people even wear it as decoration because they believe that it can bring luck and happiness for their life.
Wikipedia: Chinese Character Classification
Wikipedia: Shuang Xi
Yahoo! Knowledge: Origin of Hei (Chinese)