Anything that calls attention to the fact that the window is not an opening helps!
The decals are meant to represent another bird or a something coming from that direction and therefore not a good choice - go the other way.
The reality is that at some point, something will trigger the flight response and regardless of what may be defining the window or wall, etc... Our fleeing parrots will hit it a near full flight speed!
At least once a month, I complete a full Real Estate Agent Tour of our home with our Amazon. Especially if anything new appears. As part of the tour, I walk through safe flight paths to other rooms and from those rooms back. Locating all windows, doors, mirrors, hanging pictures, etc...
The flight response is so hard wired, the only thing we can do is to provide safe avenues. With our Amazon, it needs to be at least two rooms in length.