Mode S is a totally new system not used yet by anybody (properly). It involves full interactions between pilots and ATC without the use of comms RTF.
At Swanwick we are able to remove anything we want including the callsign (why???????), however, understandably most removals aren't permitted. This applies for both foreground and background tracks. The former being the traffic working/worked/to work a sector, the latter being traffic a sector is uninterested in.