Many places are starting to ask for an upfront "donation" to help offset the costs of volunteer training and other materials (t-shirts, name badges, etc) that you may be issued. It's also a way for groups to seperate the people who REALLY want to volunteer from the people who sign up, go through training, get their t-shirt, and then never show up to volunteer. Non-profits get a lot of people who go through training and then are never available to actually work a shift. Plus ... a lot of schools require that students do volunteer work as a requirement for classes or extracurricular points, and it could be that this particular group has had a lot of kids go through the program to get their volunteer card signed, but then they never return.
But it's not unusual -- not where I'm from, anyway.