A manually operated electric switch or pneumatic valve by means of which, on a locomotive equipped with an automatic train stop or train control device, an automatic brake application can be forestalled, or by means of which, on a locomotive equipped with an automatic cab signal device, the sounding of the cab indicator can be silenced. (49CFR236)

The following video provides you with the correct English pronunciation of the word "Acknowledging Device", to help you become a better English speaker.