You can now use a dollar sign ($) (aka cashtag) before a ticker symbol when posting about or searching for info about what others are saying about a company on Twitter.
So, to find out about what people are tweeting about Apple, search $AAPL.
For Southwest Airlines, search $LUV.
You get the idea.
See Also: Twitter unveils ‘cashtags’ to track stock symbols (via CNNMoney)
Note: Use of the $ is not new is not new. A service named StockTwits has been using the symbol for years four years the CEO has shared some thoughts on the topic. He says Twitter “hijacked” the idea.