An anthem, that's good.
How about a tie pin? not many wear ties these days let alone a tie pin.
A very small lapel badge or even a sticker somewhere with an eagle on it. Of course representing clear vision, power and renewal.
Sisters could use a sleeping beauty reference to indicate the awakened state or an owl brooch, symbol of the Goddess Athena meaning wisdom.
All PIMOs could all use non NWT Bibles. Of course purely for the purpose of knowing what church goers are used to hearing and therefore useful in the field service.
A pinkie ring with the flat piece inwards.
Navy coloured shoes for males or blue tights for sisters . Blue stockings having a reference to literary minded or intellectual women.
Any more ideas?
The object though is to have something which would intuitively connect PIMOs, the game is lost if PIMIs understood what was going on.