The requirement for PFD's is normally found in the sailing instructions.

The NOR is used to communicate basic information for the decision to enter a race.

The SI's are used to communicate the intentions of the RC and the obligations of the competitors.

The Hobie Class Rules specify the type of PFD, not that it be worn. That is either done via the SI's ("PDF's shall be worn at all times while racing" or "PFD's shall be worn at all times while on the water except brief periods while changing clothing") or by the display of code flag "Y" no later than the warning signal of a race (RRS 40.1).