This is quite a fascinating debate around the topic of trademarking hashtags (particularly for Twitter, but I imagine this extends to other platforms such as Instagram too). 

I can understand how it has come to pass: you've spent time crafting a specific hashtag for your brand, only for a competitor or random user to start using it either to promote their own work, or for something unrelated. That practice is called hashjacking. Frustrating, right?

The trouble is, how do you really police this? How do you draw the line to say that x person can use it, but another cannot? Will a trademark make users more reluctant to use it (even correctly)? How will a trademarked hashtag be easily identified?

It'll be fascinating to see how this develops in years to come.