The derailing of a topic is going to be hard to enforce. These threads, just like real-life conversations often stray from the original topic. Sometimes not so good, but most of the time very interesting. JMO.
As to the political avatars & sigs, I don't see a problem with someone having a positive image of our President, or any other political figure. One that is in bad taste is a whole other thing.
There's my $0.02.