When a user - for example - creates a new social group and for this group the addon creates a new subforum, this won´t be checked automaticly by the routine and signatures won´t be visible there. So the staff would have to check each and every day for newly created groups (and their forums) to include them in the settings, since the group creators and the group members will complain over and over, why signatures aren´t available.
There is an absolute easy fix to get rid of that workload: instead of having that nodes list showing forums to be included, make it a list which nodes to exclude.