Thanks Meter 593
Join Date: Feb 2011
Location: East of Seattle
That looks like T-Mobile official stock rom. What is the second icon from the left in the notification screen? I will get green lights for notifications frequently but you state that there are none waiting for you.
You may wish to run a virus scan app but I doubt that it is virus related. It would be a moron of malware author to activate a flashing light indicating that he is ripping you off. I'd check on recently updated apps and see if turning them off in settings one at a time will let you isolate which one is causing the flashing light.
The other thing you could do is check to see what apps are using more background data than usual.
If after all is said and done you are still worried, factory reset and start over.
Hastily spouted for your befuddlement