First of all, the best information that I have is that the Cobra Dane is still functioning. It's no longer serving in the space surveillance and missile warning modes but instead is being operated by contractors to perform its primary mission - gathering intelligence data on Russian missile tests. I spent a year on Shemya as a Cobra Dane crew commander so I try to keep up on the system's status.

Second, an unmodulated carrier might not be distinguishable for any other radio signal. However, if it does show signs of pulse or frequency modulation then you'd have a much stronger case for artificiality. AM is not necessarily a good indicator because many things can affect a signal's amplitude. However, pulses or frequency shifts are another matter.