Mainly this means that the Sentinel should set up a safe place for Pylon activities to occur. It may also mean the unpleasant task of removing disruptive elements from the Pylon. The Sentinel may establish whatever dress code or regulations he or she desires within the Pylon in order that it might meet without attracting undue notice. In this function the Sentinel must know his of her community. If you meet in the heart of a white bread suburb, the yuppie look is probably better.
Magical misdirection is a skill.
The Pylon serves as a secure wall to persons within. If the Sentinel has done his or her job, then the seriousness of the Initiates is all that matters. If they pursue their Initiation, they will seize upon the Pylon for their needs. They can write rituals, lead discussion groups, make road trips to museums, set up mini-conclaves, etc. The Sentinel should not have a greater or lesser role in this than the others, and should use his or her office merely to be sure that no one person takes up all of the time.