No sig
.....So, where we (non-US types) consider their use of the term 'emergency' non-standard, it is approved phrasology in the US system.
It should also be noted that a controller can initiate an emergency response on their own authority with no "Mayday" or "Emergency" call being made whether the aircraft is in flight or on the ground. Plain-language "Smoke in the cockpit" would be enough to warrant that.