At this moment there are two switches whether you are allowed to signup.
1) Is the signup functionality enabled for this node located on the node form.
2) Is the signup list still open or closed on the signups tab.
At this moment only the second switch is stored in the database. Therefor it is not possible to actually 'disable' the functionality if a node type has the signup functionality default enabled. I think the solution is to save a bit with 'enabled' and store it in the database per node. Is this correct?