You could go for a large circle, and inside that are two equally sized circles with diamters 1/2 of the larger circle, so the two circles were lined up next to eachother and tangental to eachother and the edge of the circle. Simple, yet obviosly boobs, yet also ambiguous enough to not be.
Like:
(OO) with the () being the edges of a circle that goes around the two OOs. Just imagine all the lines connect.
I seldom fling children from towers to improve their health.