I know this is a little late for the one school, but I'm adding it anyway. Different schools and clubs have different practices, whatever you may want. Some, especially very traditional dojos, may expect you to watch a few classes before asking if you'd like to participate. In fact, they may ask to meet you somewhere else, like for coffee, before they bring you into the school at all. This is a mutual sizing up; they're deciding if you're someone they want around, and giving you a chance to decide if they're a place that you'll want to commit time to. Don't worry too much, though -- this is kind of rare in the US and Canada, except for training halls you'd really have to hunt for.
I generally size up visitors, and depending on their comfort, will invite them to train the first time they come to class. If they just want to watch, that's fine, too.
If offered, I'd encourage you to participate in the training. It'll give a much better feel for the place than simply watching is likely to. Liken it to buying a car. You can buy a car without doing a test drive -- but wouldn't you generally be more comfortable with the purchase to test drive it first?
