this picture was taken in flight of the Garmin 696 moving map display, and shows two aircraft "TRAFFIC" indicators off to the right of our aircraft.
Velocity vector on TRAFFIC shows direction of flight
+XX indicated means the TRAFFIC is +XX hundred feet ABOVE our aircraft.
-YY indicated means the TRAFFIC is -YY hundred feet BELOW our aircraft.
In this example picture, the TRAFFIC data was supplied via ADS-B IN transmissions from FAA Ground Radio towers, which were received by a NAVWORX ADS-B OUT/IN Universal Access Transceiver (UAT).
The traffic indicators will look the same if (as another example), the traffic data is supplied to the Garmin 696 using "TIS-B" data supplied by a Garmin GTX-330 Transponder (for example). Note that TIS-B traffic may not be as complete as ADS-B IN Traffic data.
ADS-B IN data is most complete for your aircraft if your aircraft is "Participating" in the Next Gen FAA Air Traffic Control system, by transmitting Valid ADS-B OUT data from your aircraft.