Like in topic - what does the half green/half Grey poison icon stands for?
It gives you resistance to that condition (so you flip the token when you are going to receive it, 50% chance to get the poison).
Hellfire PA has the same icon but with burning, so the same.
DK-dark has it correct. The symbol means that character is resistant to the condition in question (in this case, poison). This would mean at the point you would normally suffer that condition, you flip the Luck token - on the Clover Side, you don’t suffer the side effects. On the other side, you suffer the effects as normal.