> In very, very broad US-centric* strokes: Using a mark in trade is enough to establish a defensible trademark.
Isn't that only if it's something that would actually qualify for a trademark?
For example, "Car Shop" or probably even "Hamburgers USA" would not qualify for a trademark due to being overly generic/descriptive (in many jurisdictions).
Now in Notepad++'s case the inclusion of the ++ obviously means it would indeed qualify.
Just asking as I'm sure there's people around here with personal experience around the topic, though again it can differ quite a bit by country.