So something like PRISM that targets everybody won't trigger a warning?
Keep in mind this will only work for non-court-gag-ordered instances. If the US subpoenas Apple about an individual they won't be allowed to notify them.
I have no idea how this applies to other countries.
I think this is more like: "We noticed unusual API usage and we don't have a gag order so whatever it is, it's not likely to be good"