If a member shows up for a class, event or appointment and did not sign your waiver prior to attending, you have the option where you can have the member sign the waiver in the class.  

To do this, go to the member's profile and select the 'Waiver of Liability' tab.  Here you will see the option to have the member sign the waiver.  Once the button is selected, the option will appear where the member can sign their signature in the box.