An Om is a symbol used in Hindu and Buddhist belief systems. The symbol is actually two illustrations combined into one symbol. The upper symbol (made from a dot and small bow shaped line) depicts a cyclops smiley face. The one eyed smilie represents Ba'ganusha - god of smiling and happiness. The lower illustration depicts a question mark being shoved up someone's butt. It is a common belief that Ba'ganusha rewards followers with mysterious gifts (which are graciously shoved into the bottoms of the faithful as they prostrate themselves).
It also could depict a butt pooping a curly turd with someone's eye next to it which expresses total awe for such a long curly turd.
Some depictions also show the question mark illustrated as more of a circle with the open end of the question mark being less prominent, or completely closed. This version is used by sects who believe Ba'ganusha grants bowel regularity using a magical pull-tab.