It is not the booking ref that you should look at but rather the ticket itself. On a paper ticket, after the flight number and before the date, there will be a letter (under class/date). This will be the class in which the flight is booked. It normally (but not always) corresponds to the first letter of the Fare Basis (in a box just above the date/class box).
On an e-ticket, the information will be displayed slightly differently. Look for a column or line saying 'class' and consisting of a single letter in the data. If you can't find this, try to find something that says fare basis and the first letter of the fare basis is usually the booking class.