[metanoia]

Exactly this. An infrared flare from a missile launch, seen from a launch detection satellite, looks exactly the same, 20kt or 450kt warhead.

[catalogia]

I'm pretty sure that only applies to ballistic missiles though. Cruise missiles probably don't show up on those satellites, and even if they did, how would you differentiate a nuclear armed cruise missile from a conventional cruise missile? There is also the matter of nuclear torpedoes, bombs dropped from planes, bombs placed by special forces (https://en.wikipedia.org/wiki/Special_Atomic_Demolition_Muni...), nuclear artillery shells (https://en.wikipedia.org/wiki/W48), recoilless guns (https://en.wikipedia.org/wiki/Davy_Crockett_(nuclear_device)), etc.

[metanoia]

The OP was about sub-launched ballistic missiles - I was trying to make the point that when a ballistic missile flies from a sub, you cannot tell the yield, and the potential hair trigger-response will be the same regardless of yield.

This type of weapon is essentially destabilizing, as the article said.

I agree with you on other weapons, the flight profile will be vastly different.