I don't think the issue here is whether or not it is a form of social signalling - it clearly is. Nor is the question whether social signalling is useful - aga

I don't think the issue here is whether or not it is a form of social signalling - it clearly is. Nor is the question whether social signalling is useful - again, it clearly is. Rather, the point is, social signals are often (and certainly in this case) based on symbolic value, which means that they may be open to "semantic hacking" that transfers that value to a less damaging alternative. That doesn't mean that the value of a diamond is unconnected with its physical properties. It is likely that diamonds are "special" because they are rare, hard, shiny, etc - all of which helped diamonds achieve their niche. But that is an historical explanation. The social signalling (that you want to indicate to someone their value to you) could be done equally well by some other "symbol" if a common social understanding can be constructed. So it's interesting because (1) hacking social systems is inherently interesting and (2) the diamond industry is itself associated with various negative side effects that sit uncomfortably alongside the notion of "love"...