The connection between choosing a coat of arms and being a part of the British or Spanish empires at some point in history is uncanny! At the same time, it is unsurprising considering that coats of arms in general are a medieval European invention. I guess, there is not much functional difference between the three, but you can’t call anything a coat of arms, whereas anything can practically be an emblem. To be a coat of arms, an emblem has to follow specific rules.
Here’s the source.