It has been about a century since coats of arms had any "practical" use. Their use in recent years is purely ceremonial.
I suspect that the nearest modern equivalent in common use is football strips, but read on
If you cast your imagination back perhaps 800 years, you will discover a Europe in which the influence of the Roman Empire had been forgotten, as hordes better equipped militarily coming from the East had all but dismantled the Empire. (The learnings, by the way, remained, but were passed on primarily only in the Arabian world for several more Centuries.)