The "primary" indicator was length of ring finger relative to index finger, as in - https://www.sciencemag.org/news/2019/06/talk-hand-scientists... - at the time, this was considered cutting edge...I understand it has been mostly discredited now.

You have also misunderstood slightly. It wasn't stuff like scars, or things correlated to wealth (or race...much good that would do in Northern Ireland or the Basque...I take it you don't know much about terrorism). It was purely body measurements iirc.