There are no decals I am aware of, that indicate whether or not it is EFI or specifically what year it is.
The SSS decal doesn't sound like it is factory.
All EFI samurais have square vent dashes, but not all square vent dashes are EFI.
It is pretty simple to tell whether or not the samurai is EFI, by looking at the engine (although, the samurai throttle body injection looks like a carb to some people
).
Another way to determine the year is to look at the VIN and run it through a free online VIN decoder. The VIN is stamped on the outside of the frame, behind the right front tire and also on a plate on the drivers end of the dash. There should also be another plate either on the end of the dash or on the drivers side kick panel that indicates the build date (month/year). From that you can also determine what model year it is (note, that the build "year" doesn't always indicate the model year).