As pushrod stated , it is an indication of a fault detected in the trans. Have it scanned (NOT a code reader!), Depending on mileage and general condition of trans. it could be anything from a simple pressure switch , to a code 'P0740'. Whatever it is post the specific DTC(s) on a reply here and I can offer some suggestion on what to do.
I am only aware of two reasons that lights will blink on and off,( except for the obvious turn and "e" flashers). 1.The ground on the light bulb is not making good contact............. 2.The element, this is the little squiggly wire inside of the light that illuminates when current runs though it. The element becomes detached and when the bulb is moving the element intermittently connects and disconnects causing the light to act like a signal light, except that it would flash erratic.