In Printed Circuit Board design, Fiducial marks are used to align the pick and place machine with the PCB. A fiducial requires a circular area free of silkscreen and solderpaste, and in the middle of that area is a smaller circle exposing the top metal of the PCB.
Creating these in Altium with keepouts can be problematic because it will create a keepout on both layers when typically you only want the keepout on the same layer as the fiducial.
I recently saw a great solution for this: do it with a clearance rule. Create a Clearance design rule named "FiducialClearance" (or whatever you want to name it) that specifies the 26mil clearance
needed and is limited to just your fiducials. Create a new rule with the following:
Obviously, replace 'Fiducial-40mil' with the name of your fiducial footprint.
Finally change the priority of the "FiducialClearance" rule so that Priority=1.