This photo above shows how wide a permit really is. You can also see how that wide side, when exposed to the sunlight puts off a huge flash of light. This reflection of light can and often does reveal a permits location from a great distance to a hunting permit angler.
As a permit feeds the fish will angle its head down on the bottom exposing its broad side to the sun. When this happens a flash can occur giving away its location.
The best thing about seeing a flashing permit is that you know that in most cases the permit is feeding. And a feeding permit means higher odds of an eat with a properly presented fly.