No luck. With the help of a librarian, I looked through two Spanish and one English dictionary. We were unable to find the symbol, or anything like the symbol.
I re-reviewed the rest of the print book and did not find the symbol used anywhere else and there is no other reference to it in the print text. (Note: there are no diacritics in this print book, so it probably isn't a macron.)
Whatever the symbol is... I think it would be of limited benefit to the reader since it does not appear anywhere else in this text, no questions are asked about it, and it is not needed for the reader to answer the questions. So, I think that I should omit it. What do I need to do to indicate the omission?