This was the best pic I could find but following the dribs and drabs coming out, it looks like it’s the Clapperboard signalling CUT  for state sponsored property purchase gains/ duck-houses/ moat cleaning/ porn DVDs/ gingernut biccies/ keeping it the family regarding staffing arrangements.

Opening titles for the cinema-themed Granada show of yesteryear are here (1981 version) while a whole episode (from that golden year 1972) is a click away here.