I'm not sure if this will be possible with just an overlay but I think it would be cool to be able to mark certain items as "keep", so that auto salvage doesn't destroy them.
I understand you could setup a full pickit definition to do this automatically and/or not even pick them up, but it would be a nice feature anyway.
Feel free to delete this if this feature is already implemented and I was just too ignorant to find it. Thanks!