Years ago the "HDPP" trucks were easily identified by the 7-lug wheels, and for a few years, an "F250" badge on the F150 body style (as opposed to an F250 badge on the Super Duty body style).
As far as I know, the HDPP trucks made in the last several years are visually identical to any other F150 on the road. The only way to identify them is to look at the stickers.
I take it Ford does not have a sticker in the glove compartment with all the option packages? With a GM all you need to know is the 3-letter/digit option code, and whether it appears on the glove compartment sticker.