What do you mean by that?

part of the initial distribution we had tokens set aside for a bounty fund. This is used for prizes, promotion, and hiring. By hiring I mean if we wanted something done we could offer STEM tokens in exchange.

How should one prove that it's he/she who brought the user to StemGeeks?

There is no easy way. Hence the relatively moderate prize, but there are referrals now that can show who referred someone via Hive Onboarding.