sometimes its hard to tell if you dont get a good look. But if you get a good close look or get to observe them with binocs or sumthin you can usually tell. Button bucks generally appear bulkier with shorter faces.
heres 4 button bucks (roughly 6 months old) notice how they look nice and stocky and the heads/faces look short. You can also see the bumps right behind and above the eyes.
heres a yearling does for comparison...looks much more thin and delicate...hahaha atleast to me
** I almost got him but I refuse to take a marginal shot **