I don't want to drop anvils from out of nowhere, I want to drop them from orbit!

The real challenge is aiming them. not that there won't be
enough collateral damage, mind you.
I have to agree with Mad Scientist. There's plenty of ocean for a Ballistic missile to be launched at many potential adversaries without Russia or
China caring enough about that part of the world to even bother looking. However, unless we are attacking say, Madagascar or New Zealand, That
missile will eventually climb high enough that they can see it. It will not be challenging though to determine that it isn't heading thier way. If
it is, then apparently we're at war already, and the worst case scenarios mentioned are already in full effect prior to launch.