The Use of Hashtags and the IOC's Trademark Rights.

The American Olympic Committee (USCO) is attempting to prevent certain companies from using official hashtags, such as #TeamUSA and #Rio2016 on Twitter. In recent weeks, the USOC has sent letters to athlete-sponsored companies (who are not official sponsors of the Games), alleging that the mere mention of #Rio2016 infringes on USCO-owned trademark rights.
One such letter, written by the USOC, states: "Companies may not post comments about the Games via their corporate social media accounts. This restriction includes the use of USOC-owned trademarks such as #Rio2016 and #TeamUSA."

The (rather rigid) approach aims to protect sponsors – such as Coca-Cola, McDonald's, GE, P&G, Visa and Samsung – who have invested significant sums to be accredited as official sponsors of the well-known sporting event. 

In the United States, it has been possible to register a hashtag as a trademark since 2013, but the application of trademark law to such distinctive signs may in some cases prove ineffective in protecting a distinctive sign marked with the “hashtag” sign.

In fact, trademark infringement occurs when a party uses a trademark with the aim of confusing the public as to the origin of a product or service being marketed.

However, not every time a hashtag is used, it's meant to distinguish a product or service from a competitor's. In fact, it can be used solely to make statements within a forum. After all, how else can you indicate that you're talking about the 2016 Rio Olympics without using #Rio2016?