You will start to notice things, like stems on most English pipes taper down to a long thin reed almost. Italian and Danish pipes don't.
On this one, if you
Google Celius freehand pipes, you will notice how the stemwork here on this one (where the stem meets the stummel) looks like most of the pipes made by Celius, whereas most Danish freehands have stems that look like they were just generic stems jammed in for no rhyme or reason.
Italian pipes have more contrast between thick and thin parts, whereas Danish pipes don't even care if they are symmetrical or not.
But, not all pipes fit the icon, so wild guessing helps too. But, things like this help me to notice these characteristics.