I label "alpha's" by a 3 observation rule:

1: clothing style, cleanliness.

2: attitude and prescence in the room.

3: popularity with both genders.

If all 3 are high on a scale of 1 - 10 say 6+, then i classify them as an alpha and a threat. I measure women on a similar scale but also add in personality as i discovered long ago that some women can be gorgeous but utter bitches when you talk to them. So i observe the social dynamics of the room and tend to approach the more relaxed, approachable and polite women, as they tend to be in a happier mood.