One way to expore the possibilities of a real life karma system would be to limit it to a select community, like we have on LessWrong, but not limited to activity on a single web site. Members would be able to give each other positive or negative karma for any activities they thought worth it. Technically, the whole thing would be managed by a server accessible over the web, by a smartphone app, and in any other way that would reduce trivial inconveniences in using the system.

Membership would be by acclamation: anyone asking to join would first have a karma account opened for them by their sponsor, and existing members invited to add or remove karma. On reaching some threshold within some period of time, the applicant would be admitted.

Members could covertly indicate their membership by displaying some secret symbol on Facebook pages, clothing, tattoos, and the like.