To me, the idea does not sound promising, for three reasons:
1. It's not subtle. Bombers and bombs coming from nowhere? How the hell does ANYONE cover that up? I'd love the historical background justification for this object.
2. It sounds very useful. All you'd need is a way to remotely activate the siren, and you'd be able call airstrikes anywhere. As a big fan of the Shock and Awe style of military warfare, let me tell you that being able to call airstrikes anywhere is a wonderful thing. However, pretty much every other useful SCP in these archives has some kind of a cost. The obvious cost for this siren is "you get bombed too," but that can easily be avoided.
3. The bomb craters just vanish? Have you thought this all the way through? What about damage to buildings? Or people?
Now, that last point might be this idea's saving grace. What if all the damage the bombers did to the landscape and buildings vanished, but the other casualties did not? It'd be quite something, to have a squadron of Badgers fly over your down and blow most of it up, killing hundreds, only for all the actual evidence of a bombing disappear a short time after, leaving you very, very confused.
