Here, look at this. This image of the AIM-120B shows the slight trail that there AIM-120 leaves behind. Yes, there is a trail. Smokeless, in other words, usually means it's exhaust plume is very hard to find in BVR combat. In FC2, I think the trail in modelled very well, the exhaust is slightly shone but doesn't have the white sheen to it like the others (AIM-9, R-73, R-27...etc.) And don't forget, it's supposed to be smokeless to your target, not to you, mostly when you're watching the missile launch.
So don't worry, we'll soon have a update/revise that will make the trail even more realistic. But again, nothing is perfect!:thumbup:
-Andrew (Revalence)