In German, nouns are capitalized whether they are proper or not. In order to distinguish between a proper noun and a common noun, Germans are forced to put their already capitalized noun in quotation marks.
In English, we can distinguish between an action plan and a Action Plan with simple capitalization, however. Our quotation marks serve a different purpose – signifying that we don't quite believe the word, a bit in the way we might say something like "so-called friends."
The result, when Germans write in English, is quotation marks around nouns already marked as proper by means of capital letters.
Today, I see that my translator colleague Jill Sommer has posted a nice cartoon along these lines.