If you just remove the link from your signup page, the surfer could always guess the check join page, the difference between the check and cc page in ccbill is sometimes just two letters...ie
check
https://bill.ccbill.com/jpost/signup...eId=0000016687
credit card
https://bill.ccbill.com/jpost/signup...eId=0000016687
You can prevent a person from changing "cc" to "ck" and gaining access to the check option by removing the check join page from the admin in ccbill.