That kind of misses the point. There are lots of neckslaces that have peace sign on them, but they're not at all a good signal of pacifism, or nuclear disarmament (what the peace sign originally stood for). Think of how many people where a ying yang because it looks cool instead of to convey an affinity, much less a dedication to, for Taoist ideals.

It is because the necklace is expensive and represents an actual (if small) step towards destroying the awful-thing, that it is good signalling.

Part of this is because the more expensive the thing and the more marginal the benefit, the more it shows dedication to the cause. This is basic commitment effects. But there's another thing. Signing up for cryonics doesn't just signal that you don't like death, it signals that you're prepared to do something about it. Complaining is common. Doing something isn't.