If the outcome of the vote is uncertain, then yes, its passage also contains information. If the outcome of the vote is a foregone conclusion, then its passage contains almost no information. In the case of Obama signing a bill he pushed hard for, everyone knew he would sign it, it was public that he would sign it, the signing itself tells nobody anything they didn't already know. If the value of a stock were going to be affected (in either direction) by this legislation, that change in value would have been factored into the price traders would be willing to pay for (or sell) the stock before the actual signing of the bill. Any trader who didn't do so would have been foolish indeed.
While it is true that the actual touching of the pen to the paper was a given once the bill was passed, there was uncertainty up until the last minute in Congress as to whether or not a compromise would be hammered out. There was uncertainty up to as much as a few weeks before if the Dems would try reconciliation to pass the bill.
Though I'm not a close watcher of the stock market, I seem to recall that the general trend of the market for the last couple of months has been upward. This would indicate that even over the time period that the outcome was unknown, the market didn't get particularly jittery, and still hasn't.
So even conceding the point that the actual signing may not have provided any sort of effect on the stock market, the general sense is that the passage of the bill has not made any Wall Street people "scared of the future", as some would have us expect.
Frankly, if anything were to shake up Dow Jones, I'd expect it to be the announcement that the Gov is working on Wall Street reforms. That doesn't seem to have slowed the recovery either. It would almost appear that a lot of the investor class think that we are on the right path, as far as their interests are concerned. Admittedly, this is no predictor of things to come, but it does indicate the complete absence of panic.
I think a lot of Republicans (those of the "I want him to fail" rhetoric of Limbaugh and his clones) are almost disappointed that the recovery is going steadily upward, if perhaps not as fast as some would wish. For my own part, I'm hoping the job market picks up soon so I can stop supporting two of my siblings.
