| Scoti Garbidis |
According to the AD&D Monster Mythology book the holy symbol is either a lobster head or black pearl.
It also states that the avatar of Blibdoolpoolp is that of a nude woman with the head of a lobster, shell covers on the shoulders and lobster claws for the hands. I think this would also work as a holy symbol.
The black pearl seems to generic for me but who am I to judge an insane group of Kuo-toan priests.