I'm in the marked for a pre-owned 2013 or newer Fusion. Most of the online listings don't have the Driver Assist package listed, but I have a feeling that's since the package is fairly new and most sellers forget or don't care to go thru that much detail.

Are there certain clues I can look for in pictures or a definitive indication on the door sticker?

 

If you can see the mirrors, driver assist will have a symbol on the upper part. This is were the light for the Bliss system will display. When a car is in your blind spot the light will come on indicating a vehicle is there. My '15 has driver assist and Bliss is part of the package.