Most N gauge layouts have either colour light signals or fixed semaphore signals. Working semaphore signals at this small scale is an art, although Ratio provide a kit that enables manual remote operation working signals. There are 2 ways of actuating the signals electrically. The first is to use Memory/Muscle Wire, and the second is to use RC servos motors. Using servos could be simpler but much more expensive than using Memory/Muscle Wire.
Another potential use for the Memory/Muscle Wire is to operate an uncoupling ramp.