well... couple ways...

for me... I can just distinguish his face from other deer.

I've been watching him grow since he was a 4 year old and his antlers made him stand out from other deer.

For someone who doesn't have a knack for recognizing deer.. you might look at the combination of the weight of his antlers with the distinct black tips of his ears...

Maybe you might notice the 30 inch wide buck missing that always frequents a certain spot one year...but notice a deer with the same mass antler and black tips on his ears with a huge spike on one side...

And then the next year you dont see the deer with the huge spike on one side but the 30 inch wide heavy buck is back with black eartips?

Pretty elementary...

I can just look at the deer and know it is him though... I could tell without antlers...

I guess it comes with a familiarity of watching him and watching video over and over...

Know how you can't tell identical twins apart... unless you are friends with them and spend a lot of time with them?

Same thing...