Coin

The chinese coin with a square hole at the centre was used since ancient time.  It is commonly used as an object as an auspicious object to bring luck/blessing or to ward off evil.  This type of coins were first made since Han Dynasty.  Uusually they have auspicious words on one side such as Tian Xia Tai Ping (天下太平）, ie peace in the world, Chang Ming fu Gui（长命富贵）ie longevity and wealth; or symbols such as tortoise/snake, crane, sword, incantation etc.　

In decorative art form, it is used mainly in rebus design. The chinese word for coin is (钱）which also sounds like 'in front'（前）.  Usually used with bats (symbolisng blessings) to convey the meaning of blessings ahead.  In ancient time, coin is also called quan (泉）and hence also used as a homophone for complete（全). Usually depicted as coins linked in a circle to symbolise completeness in things auspicious.