The abbreviations “AM” (a.m.) und “PM” (p.m.) can be found pretty often on digital watches. They are coming from Latin words. AM means “ante meridiem” in English “for midday”. PM comes from “post meridiem”, which “after midday”.
The AM and the PM display will be used when a digital watch can only show the numbers 1 to 12. AM or PM appears next to it to be able to differentiate morning and afternoon or evening.
There are exceptions (e.g. the “Ibiza Ride” of Binary) showing either the AM or the PM display. When the corresponding display doesn’t appear, it concerns logically the time of the day which won’t be displayed.
The following pictures of a digital watch show left and right the same time. On the left side it is 09:31 PM on the right side 21:31.