Yep. very shallow groove.
After a bit of googling:
Dont think it is a compound change as edge compound is shown further out on both sides of the tyre on Bridgestone website.
But came across just two references to this:-
http://www.motorcyclenews.com/MCN/Pr..._/R-EPI-130405
A static disipating line ? Can anyone else confirm this?
If so then whatever material it is wears easier than the tyre compond it is in.