It appears that what is looked for is an indication of the state of acceleration or deceleration of a vehicle. It also seems desirable to have this independant of the vehicle's mechanism.
If a basic , low cost single axis accelerometer can be combined with an indicator light such a device can be mounted anywhere.
The site below describes a simple mechanism for measuring vehicle acceleration.
http://www.exo.net/~pauld/books/car_sci ... meter.html
It would be a simple matter to rigidise this by using a rigid rod instead of a string to support the weight. The pivot of the pendulum can be attached to a potentiometer, which is at the midpoint in the zero acceleration positon. When the vehicle decelerates the pot rotates in one direction and in the opposite direction when it is accelerating.
The amount of deflection is related to the amount of acceleration or deceleration.
By combining this info with two-colour LEDs (Many available) it should be possible to produce a low cost indicator, which will show(for example) increasingly bright green when accelerating and increasingly bright red when decelerating controlled by the level of action.
Since the components are low cost it should be possible to retail this at below USD 60 with a tidy margin.