I can only assume that the writer wanted the reader to understand that he meant "design" as a verb, not as a noun in that particular context. Personally, I don't really see what difference it makes!
Writers will sometimes put (Note: XXXX) after a word or a phrase asking the reader to "take note of" whatever comes next.
For example, might write:
Capitalisation (note: BrE spelling) is very important.
I want the reader to note that "capitalisation" is the BrE spelling of the word which in AmE is "capitalization".
Student or Learner