This is a textbook question but I did get an answer for you from Mary Ann Damm. 🙂
If I understand the question, the bracket is a symbol used throughout the book to identify specific paragraphs. So forget that it is an enclosure symbol; it is not being used as one. Use the shape indicator with an appropriate symbol (letter "b" for bracket or "p" for paragraph, for instance). Explain on TN page and put the symbol on SS page. Look in Rule 5, Section 3.
Hope this is helpful! Happy Holidays!