Why is the financial aid office at my university asking for my parents' signed tax returns...?

Oh dont worry, you were just chosen for verification. There are a few reasons why you could be chosen but mostly its because each college has to randomly choose 1/3 of their students and ask for documents to verify that what you put on your FAFSA is true. That is how they make sure the majority of people do not lie on the forms. Or they can do it if they see something they want to verify. We had to do the same thing. We do our taxes efile so we were told to just print them off and then sign the bottom. Also, if you live close take them there otherwise send them via post office return receipt because that way you get a notification they received it and its safer because those tax forms have ssns.

They want to verify your parents income and that your are a dependent. They are making sure you qualify for the financial aid you receive. If your parents report substantially more income than you stated in your financial aid application you may lose assistance.

Relax. Colleges do this to verify you/your family's income in order to see if you qualify for need-based scholarships, and, if so, how much.