I’m not an expert in House rules, so I can’t cite you a rule. I’ll take the Capitol Police reports just cited as enough evidence that there isn’t a specific rule against wearing t-shirts.
If there isn’t a rule against such a thing, then it looks like the Capitol Police goofed up in sending both Sheehan and Mrs. Young out of the galleries. However, I would still maintain that if the House wanted to make a blanket rule against observers wearing political slogans while in the galleries – whether it is “stop the war,” “support the troops,” “vote Republican,” or whatever – I think it’s perfectly fine to establish standards of decorum in places like courtrooms, the chambers of Congress, the White House, and so on.
Hell, if Congress wanted to make a dress code that gentlemen must wear a tie and so on, I think that’d be just fine, too. As I said before, that seems like the kind of rule that should be enforced by kicking people out, not arresting them.
What I don’t think is fair to say is what Crooks and Liars stated, namely, that “It was a blatant attempt to control the environment where our fearless leader appears as usual.” I fail to see how if that is the case, why Mrs. Young would be thrown out, too. Was Mrs. Young a threat to the environment of the fearless leader? Hardly! A breach of decorum? I think so. A crime? It shouldn’t be.
(I’m also curious as to why the Capitol Police would be asking the charges against her to be dropped if she wasn’t arrested, but the question appears moot.)
As I said, I’m not a lawyer, but I seem to recall that the courts decided long ago that Congress is acting within its authority by establishing a morning prayer, regardsless of what the First Amendment says. Furthermore, I’d be very surprised if courts would find that ordinary people are allowed to engage in protests on the Floor of the House, for example, even if the same assembly might be perfectly alright on the steps of the Capitol.