Usually the males are the big bears.... and there are a few ways to tell what bears are BIG. Though there are some big alone females out there also....
Square head - bigger
Flat nose - females will slant in from nose inward to lip, if the have almost an underbite where bottom lip sticks out at least to the nose, with a flat nose front, big male.
Seemingly short legs - belly down towards the ground, big bear.
Small head - means a big body.
Long neck - as in a comparison of neck length to back of skull to nose length. Longer the neck... bigger the bear.
Ears - if the ears are on top of the head, smaller bear, if ears are down more on sides, bigger bear.
Big hips - if you can see the rear end a mile away, and the front end seems small in comparison
So if you have a blocky seeminly small head with ears on the side, head that is shorter than the neck with a flat nose/lip and big gut hanging without much ground clearance and big hips, then you may as well be looking at a good boar...
But most of the time you really can't tell.