Comment by gambiting

I think the difference is that air launched missiles could carry nuclear payloads but usually don't, while ICMBs could carry non-nuclear payloads but usually don't. All kinds of countries have been using air launched missiles all the time which at least on average tells us that every time one is fired it won't(shouldn't) have a nuclear payload. ICMBs on the other hand have never been used against anyone, and their stated goal for existence is carrying nuclear payloads - so if you see one coming your way you can assume it's a nuke, even though technically it doesn't have to be.