Cue-bidding is a preferred approach to trying for slam. Once a trump suit is agreed, a new-suit bid shows a "control" there. If the auction begins one spade-three spades, four clubs, opener suggests the ace of clubs and slam interest.
The opponents may double a cue bid to ask for the lead of the suit. Then most players treat a redouble by either player as showing second-round control - the king or a singleton.
I wouldn't try this (especially if playing for money) without discussing it with my partner in advance. I might find myself playing at four clubs redoubled with A-x of trumps opposite a singleton.
When today's West doubled South's cue bid of four clubs, North's redouble promised second-round control. North-South then continued with more cue bids that showed controls in both red suits, and South bid a grand slam.
West led the king of clubs, and South took the ace and counted 12 tricks: five trumps in his hand, a club, two club ruffs in dummy, two diamonds and two hearts. He needed a trick from dummy's long diamond.
South ruffed a club at Trick Two, led a diamond to his king, and ruffed a club. He cashed the ten of trumps, took the ace of diamonds, and ruffed a diamond high. When West discarded, declarer went back to the queen of trumps and ruffed a fourth diamond. He could then draw the last trump, take the A-K of hearts, and win the 13th trick with the good diamond.