Perhaps a rating system based on proportions, symmetry, and skin health. However, I'm not convinced this is that (it is a large factor in decisions, yes, but it's not one you can change much beyond style and hygiene, unless you're willing to undergo plastic surgery) important, except in the realm of Tinder-esque situations.

If you happen to live somewhere where random people will complement you or flirt with you, I suppose number of incidents/number of people exposed to over a large span of time could be a metric.