I know that via stitching requires me to assign my vias to a signal (like GND pours on top and bottom layers).
Do I need to assign signals to the vias in order to "fence" routed nets, for example, differential lines fenced with GND vias?
it is preferred that the the fence will be assigned to GND. There is a need to separate between stripline and other srtip structures like microstrip.
In stripline the lines are between GND on top and bottom of the pcb and the vias create a good fence. on other routhing configurations where the traces are on the top layer, the GND plane is on an inner or bottom layer. there configurations are less resistant to EM interference.