None whatever! If you use rudder for anything other than maintaining balance during a stall, you are inviting a spin. 'Stopping wing drop' or, even worse, 'picking up a wing with rudder' is an archaic nonsense which should have been stamped on years ago.
Also, never let a student hold the a/c in the stall unless you are doing so to demonstrate light pre-stall buffet management if your a/c type has such a characteristic.
The student is learning to recognise and recover from the stall with minimum height loss. You show him (with him following through) the identification of the fully developed stall - buffet, nose drop, wing drop, high RoD, nodding dog or whatever, then tell him that any one of those is an indication of a fully developed stall and he should recover when he recognises any of those stall identifications.
I don't use 'signs' and 'symptoms' ever since medical stuents commented that this was bolleaux. So now it's stall warnings (keep going and I'm going to stall, idiot!) and stall identifications (I warned you, you didn't listen and now I bloody well HAVE stalled like wot I told you I was going to!).