[gwnn]

N deals and it goes
1♣-p-1♥-2♥
East alerts and North asks, East says "5-5 spades and diamonds".
3♣-
Now East reaches for something in the bidding box (presumably 3♠ - he had a 4-2-4-3 5 count), and the following silent dialogue commences
W:
E:
W:
E:
East passes.
W:

What should North or South do? These cases happen to me from time to time and it's hard to prove anything, especially if EW were not paying attention or can't recall to their facial expressions.

When should N or S call the director and what should they tell him? What are their chances?

[bluejak]

They should call the TD immediately after the silent communication and tell the TD what happened. Proof is not the point: as normal, the TD will have to make a judgement.

What are their chances? Not very good in some ways, assuming E/W deny it. But that is not the point: you call the TD for an infraction and there are two good things that can happen.

• N/S may get a ruling in their favour
  
• E/W are warned and are less likely to indulge in these antics in future

[PeterAlan]

On a detail, presumably it's East that both alerts and (not West) explains the 2♥ bid.

[gwnn]

yes I will correct the post.

[wyman]

No, you can't force them to bid. However, the director can adjust the board after, penalize EW, etc. Good luck getting a ruling in a club game, but in a national/regional event, you should be protected.