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I think it might be Voice Over LTE or Volte. Newer feature on some devices and carriers.
http://m.androidcentral.com/how-enable-volte-galaxy-s7
Can you swipe down on the drop down menu and tap the icon? Should tell you what it is.
When I swipe down there is no notification for it at all, its just there and I don't know what it means. If it helps it was there after I rooted my galaxy s7.
How did you root?
http://forum.xda-developers.com/att-galaxy-s7/how-to/g935a-root-t3410403How did you root?
http://forum.xda-developers.com/att-galaxy-s7/how-to/g935a-root-t3410403
If you look around root is available for all carriers. For the S7 and S7 edge. Verizon, AT&T , Sprint, T-mobile.
Sprint is a pain in the butt due to the activation screens.

Awesome sleuthing!!! Good find!
If you haven't straddled too far from your OEM software, read your instruction manual to see what the symbol means.Wow, I am a proponent for root but, there is some scary stuff going on in that thread. Could be a lot worse than an annoying icon
Maybe you should look though the app manager for any strange apps. If there is a constant notification then there is an app running somewhere.