Altium hide component designators in fabrication ourput gerber
To mass-hide all component designators:


Shift+F, then click on a component designator
It says Object Kind, Text, Same. Change the box String Type, Designator from "Any" to "Same"
Click OK
All component designators are selected.
In the PCB Inspector, click Hide->True
If you have some hidden already, this will Unhide all
Click again to hide all


When you want to unhide them all, go into a component dialog and uncheck Hide in the Designator area. This will give you something to click on for the Shift+F operation.