In the hotel search screen, you are able to distinguish by the green banner when a discounted rate is available for booking.  The new pricing comparison tool shows you a snapshot on this page of the lowest available discounted rate versus the lowest rack rate.

When you select begin booking and select the room type of the discounted rate, you will see the comparison populate the total savings under the rate information.  This data is then stored in your account when you complete the booking.

You may pull Reports from Requests>Search Orders and select request type "Hotel" for a date range, then download  the report.  In the excel download there are many columns with various information and you will see Column D shows the room type description along with the special rate code in Column Y. Column AC shows the discounted FlightBridge total that was booked versus the lowest rack rate or "comparison total" in column AB, and the total savings in column AD.