If you are working on drawings that will be used by subcontractors it would be best to include the call out "GTAW" in the tail of the welding symbol. You may also consider specifying the filler metal if you have a preference. For instance, if you want the contractor to use ER308 instead of ER316L, simply list "ER308" under "GTAW".
If the drawings are for internal use it makes sense to include the appropriate WPS in the tail of the welding symbol.
It makes no sense to reference a specific WPS that a subcontractor doesn't have access to.
Best regards - Al