Green’s Dictionary of Slang

1. a yellow speed bump placed in the centre of an intersection.

1934		T. Wood Cobbers 122: A circle in the middle of cross-roads, for example, round which all traffic changing direction must swing; a round yellow blob, known here as the Silent Cop, or the Poached Egg.
1948		R. Raven-Hart Canoe in Aus. 187: Motorists often ignore ‘Silent cops’ at corners, yellow domes with white surrounds, ‘poached eggs’.

2. a small female breast.

1985

‘Thommo’ Dict. Aus. Swearing & Sex Sayings 101: POACHED EGGS — Small, flat, but well rounded tits.