SFO Controller voiced concern regarding alleged ambiguous visual separation procedures applied by NCT Controller during simultaneous approaches; listing aircraft passing one another as an example.

Narrative

Both aircraft on final descending about even; maybe Air Carrier Y .1 mile ahead. Air Carrier X asked if Air Carrier Y was assigned visual separation from them? I advised I was not aware how that was done; just that they were both on visual approaches. Air Carrier X acknowledged; then Air Carrier Y keyed up and said they were not assigned anything. I asked Air Carrier X if they were assigned visual separation and they said yes. This is a huge problem. If Air Carrier X joined final slightly ahead of Air Carrier Y; I would not know that an Operator Error (OE) has occurred; I would have issued the wake turbulence advisory and let them land. The ambiguous visual separation that NCT provides creating situations where aircraft are passing each other and occasionally going around unexpectedly is unsafe at best. This is a link in the chain. I can only imagine the relief the controllers would experience if they were told one-way visuals only that is that! Recommendation; NCT should go to consistent one way visual separation on final into SFO to alleviate the ambiguity were aircraft are passing each other established on final.