What is the symbol on front of the Bus?

The markings highlight the location of the air-to-air refueling receptacle on aircraft that use the "boom and receptacle" system of air refueling. In this system (used primarily by the Air Force among the US services), the receiving aircraft flies within the reach of the refueling boom, and the tanker aircraft then guides the boom to the receiver to plug in the connection. The markings typically include some brackets that indicate the general location of the receptacle and help the boom operator to guide the boom onto the receptacle as well as a line that denotes the longitudinal centerline of the receptacle.

The markings are typically painted to contrast with the skin color of the aircraft around the receptacle. White, black, yellow, and red are common colors for the markings. There are also often lights that illuminate the area around the refueling receptacle. Some aircraft (such as the C-17) have markings that contain luminous elements.

This is a video that explains some of the basics of USAF air refueling: http://airforcelive.dodlive.mil/2015/07/video-how-aerial-refueling-works/

In contrast, the US Navy, Marine Corps, and Army aircraft that are capable of in-flight refueling typically use a "probe and drogue" system. In this system, the tanker aircraft trails a drogue or basket behind it, and the receiving aircraft flies to put their refueling probe into the basket. Since the receiving aircraft controls most of the process of plugging into the tanker, they do not have the markings associated with the receptacle-style aircraft. Usually lights on the tanker and a light near the refueling probe on the receiving aircraft facilitate locating the drogue/basket at night.

The bus is based on the Boeing C-17 Globemaster III and you can see the same emblem on that model of plane. According to various articles I've found on the Globemaster, it has surface mounted thermal sensors to aid in counter-measures. My guess is that those marking are one of the sensors.

This is just a guess, but I think the markings on the upper front of a C-17 aid in refueling the aircraft. Some variations of these markings appear on other aircraft as well, and are positioned in front of the refueling receptacle. I'm guessing these markings are there to aid the boom operator to accurately "fly the boom" into the receptacle of the receiving aircraft.