A person who only believes in the signalling value of green technologies (hybrids are trendy) does not want a social policy mandating green behavior (the behaviors would lose their signaling value.)

A social policy mandating a behavior that is typical of a subgroup shows that that subgroup wields a lot of political power and thus gives it higher status - those pesky blues will have to learn who's the boss! Hence headscarves forbidden or compulsory, recycling, "in God we trust" as a motto, etc.

If you're in a population of similar agents, you should expect other people to be doing the same thing, and you'll be a lot more likely to lose the war than if you actually fight.

I am familiar with the argument, it just happens to be I don't this this is so, at least not when it comes to coordination on global warming. I should have made that explicit though.

Any action that "promotes the social norm" but does not really enforce the behavior may be good signaling within the community, but will be useless with respect to not getting killed by barbarians.

I don't think you grok how hypocrisy works. By promoting the social norms I don't follow I make life harder for less skilled hypocrites. The harder life gets for them, the more of them should switch to just following the norms, if that happens to be cheaper.

Sufficiently skilled hypocrites are the enforcers of societal norms.

Also where does this strange idea of a norm not being really enforced come from? Of course it is! The idea that anything worthy of the name social norm isn't really enforced is an idea that's currently popular but obviously silly, mostly since it allows us to score status points by pretending to be violating long dead taboos.

The mention of hypocrisy seems to have immediately jumped a few lanes and landed in "dosen't really enforce". Ever heard of a double standard? No human society ever has worked without a few. It is perfectly possible to be a mean lean norm enforcing machine and not follow them.

A person who only believes in the signalling value of green technologies (hybrids are trendy) does not want a social policy mandating green behavior (the behaviors would lose their signaling value.)

He may not want its universal or near universal adoption (lets leave aside if its legislated or not) but it is unavoidable. That's just how fashion works, absent material constraints it drifts downwards. And since most past, present and probably most future societies are not middle class dominated societies, one can easily argue that lower classes embracing ecological conspicuousness might do more good. Consuming products based on how they judge it (mass consumption is still what drives the economy) and voting on it (since votes are signalling affiliation in the first approximation).

Also at the end of the day well of people still often cooperate on measures such as mandatory school uniforms.