Green’s Dictionary of Slang

dubs n.2

[abbr. SE doubles]

(Aus.) marbles.

[US]E. Wittmann ‘Clipped Words’ in DN IV:ii 119: dubs, from double. ‘Dubs’ means ‘doubles’, or two ‘men’ (marbles).
[Aus]Baker Popular Dict. Aus. Sl. 26: Dubs, marbles which are placed in a ring in a game of marbles.