Professional mixed martial artists are highly trained professionals in all areas of self-defense and combat; making it all the more incredible that some of these guys can master specific techniques and use them effectively against world-class competition.
A signature move means they have used the move multiple times with effectiveness, thus identifying the move with that specific fighter and vice versa.
Using a move once, even if iconic, does not make it a signature move for the purposes of this list.
Machida landing the front kick on Randy Couture was amazing, but not necessarily a signature move since we do not see him use it to great effect on a regular basis.
The same could be said for Frank Mir's armbar over Tim Sylvia or John Makdessi's spinning back fist over Kyle Watson.
That also means no inverted triangles, showtime kicks, or pace chokes.
That being said, please let me know what I missed.