”Amgen’s osteoporosis drug Prolia not even approved yet,but co has full-pg Parade mag ad:”Discover Truth About Osteo” $AMGN via @mhuckman.”

If you’re discussing something Google is doing with its algorithm or Google labs, why not include $GOOG? If you’re discussing Windows 7 or Bing, why not include $MSFT? Or $RHT if you’re tweeting about Linux OS? Like something Amazon did? When you tweet, include $AMZN.
In this case it serves as a type of hashtag in speaking to a larger readership (such as the people following conversations about those stocks in their portfolio). The twitter third-party app “Stocktwits,” created by Howard Lindzon, which is incorporated within Tweetdeck, serves as a clearinghouse for all stock ticker symbol-related tweets.

Obviously this should only be used if you are actually conversing about the company in question: you’re providing news and information about the company, either first-hand or by repeating from a news source, so this can useful to investors. If you’re an officer of the company, there may be reasons why you might not want to include your ticker symbol in tweets about internal news, projects, ventures: possibly SEC communications regulations involved there, about how and when news can be transmitted to avoid the appearance of a ”solicitation to buy stock.”

But for most of us, a legitimate value-add to the inclusion of the stock symbol is knowing you’re joining a larger conversation and can add something to it. Your reward for the effort is a much, much higher probability of your tweet being indexed by the ‘bots. If your tweet links specifically to a relevant blog post, this has SEO value (provided your shortener is the right type).

Lastly, if you’re doing work with a non-profit and you want to broadcast thanks to a publicly-traded sponsor, while also promoting the non-profit’s work to new readers, including the ticker symbol in an appropriate context within the tweet can help you  accomplish both.