How can you inform Dartmouth that you are a legacy student?

I don't know if this will even help my application, but my grandfather went to Dartmouth and I was hoping they would ask for that sort of thing on the application. However, unlike most of the schools I am applying to, I don't see a place where I can add it in. Am I just missing something or do they really not ask? If so, is there any way I can tell them anyway? Thanks for your help :]