2 fawns together, the bigger one will almost always be a BB.

Squarer blocky head.

Single, smaller deer will often be a BB.

NUBS on the head!! If any doubt, let them walk.

1st few years, I shot several - dumbest deer in the woods. Learning to be patient and observe, it's been 3 years since shooting one.
I personally think that requiring the use of your buck tag on one would protect far more bucks then any kind of mandatory AR.

Steve