Assuming you mean Sallie Mae's "Smart Option" loan, I just wanted to issue a warning: These loans require repayment WHILE YOU ARE IN SCHOOL. Sallie no longer offers the payment deferred Signature Loans unless you already had one and are still subject to its previous terms.
If you become unable to make payments on this while you are in schhol, then you will default and your cosigner will be responsible for payments. If your cosigner can't make the payments either, then his/her credit will be affected.