That is a "camper special" emblem from a 73-87 squarebody - Typically they were on the corner of the cab band but some truck had the emblem alone. They were also accompanied with the script "Camper Special" or "Trailering Special" and the GVWR below them on the bodyline. Kinda a throwback to the days when manufacturer's cared about packages for hauling campers - GM even had camper tie-downs, stabilizer packages and upgraded suspensions for this. I wish they still did it.
And yeah, the bodyline. Always a frustration of mine, particularly since the rear part of the cab is the same as a regular cab. HUGE oversight.