The simplest solution, in my opinion, may be to not count posts in this board (in addition to Off-topic) as part of the activity and hide the signatures, a model closer to serious discussions. Then, with a little management, this board will be a place for those who want to discuss these political, although I believe that the goal of it is to discuss bitcoin-related political topics not purely political.
Since we're in Bitcoin forum, any discussion should be related to Bitcoin, otherwise it should be moved to off topic.
But the thing is, if someone create a topic about politic or society related to Bitcoin, they can post in other boards because it's still appropriate.
Discussing China allow Bitcoin can be posted in legal board, discussing about Russian invasion to Ukraine and Bitcoin price can be posted in economy or speculation board.
I disagree for ban signature in Politics and Society board because this board has low traffic, banning the signature will make the traffic lower.