Grasscutter
There are Wiki Pages on Mode S.
Simple reason is smaller aircraft like the flybe fleet tend to have Mode S which just broadcasts height, callsign etc, but does not broadcast position. ATC units still need secondary surveillance radar to identify the position of these aircraft. These aircraft will not display a globe next to them on radarbox aircraft details, and as the box is not a real radar, it cannot plot the position of these.
Mode S ADS-B adds to the message broadcast from the aircraft with the position coordinates. ADS-B is mostly carried by larger aircraft (above 737 size) although its use is becoming more widespread. As the Aircraft broadcasts a position, this is what the radarbox uses to plot it on the map. If radarbox picks up the ADS-B position signals you get the globe next to them on the radarbox details.
Mode S: aircraft not broadcasting position details = no globe, aircraft will not plot on map, will not be on network
Mode S ADS-B: aircraft is broadcasting position details = globe, aircraft plotting on map, is on network