What the hell does censored alex Lifreson say ?

I don't know, but the band claims it's a joke. Personally I think maybe Alex was a little tipsy or on something and said something that they didn't want to be broadcasted. If you notice right afterwards Geddy keeps hitting his hand to his head in a comical way, perhaps mocking what Alex did. Who knows? I still love em....

http://nimitz.net/rush/faq3ans.html#123

What is happening during the "censored" section of the A Show Of Hands video?

"That's kind of a joke, but it doesn't seem like many people are getting that joke. Actually, Alex, at certain parts of that song, would just start rambling into the microphone - all kinds of various nonsense, and it actually never got recorded anywhere. So no one had any idea, including him, what he had actually said. But we loved the shot of him just ranting into this microphone, so we decided we would put up this bogus 'radioactive' warning about the fact that we had 'censored' what he had said, and we thought we did it in kind of an obvious way - it looked like it was phony, because we put the radioactivity symbols right on the screen, but nobody seems to be getting that." - Geddy Lee, in the 12/4/89 "Rockline" interview

Alex laughs. "I'm not singing, it's more spontaneous babbling! You get kinda goofy at the end of a show, especially near the end of a lengthy tour. That was just crazy rambling, verbal farting. It was Geddy's idea to put it on the video." - Alex Lifeson, in the April 1992 Kerrang interview

http://nimitz.net/rush/faq3ans.html#12