I use the tiger as the mascot because tiger is almost "recurring" figure in the novel, in both animal and name. For example, Wu Song (on K, Club card) beat up a tiger and he's called "Tiger Killer". Li Kui (on J, Club card) slain four tigers for eating his aging mother. Gu Dasao (on Q, Diamond card) has nickname, "Female Tiger" due to her temper and violence. Many other characters (not appear on cards) has "tiger" in their nickname.
Rickshaw is a nod to Bicycle Playing Cards brand and the angel (fairy?) riding penny-farthing on their back design. Since this is Asian theme, rickshaw is used. The Chinese words on the tuck box design literally means "Water Margin Vehicle (with wheels)" ;)