Human breasts---and in particular their maintaining significant volume even when not needed for feeding offspring---are very much a signal.

[...]

Breasts implants break this signal. We can predict that if breast implants were free and available to all hunter gatherers that such tribes would soon evolve to be less attracted to breasts.

I understand there may be some debate about the actual purpose of breasts, which is why I phrased this as a hypothetical, but I think I should make it clear that the evolutionary pressures that led to men preferring breasts are separate to the question of whether men are actually evaluating fertility (or whatever) or simply enjoy large breasts for their own sake.