It means Hearts, Spades, Diamonds or Clubs.

Well, these are all clubs, these are all spades and these are all hearts.

If the cards drawn are of the same rank, the suits decide the higher rank in this order: spades (high), hearts, diamonds, and clubs.

The diamonds and Club designs also have interesting stories.

Of course, parents, children, and siblings ­exchange other gifts too, but you give plum cakes to other families.