SIGs have a documented process to be created, but tbh is very lightweight, because being in a SIG basically means that you are working with some people in a common thing. THat thing could be as little as a common application, or as big as the Join SIG that welcome all newcomers.
FAS groups needs to be requested to via ticket. So basically is at discretion of the infra team what FAS groups are created, but as we are saying in here, everyone always assume good faith on everyone.