The signal is 3 times the noise level of an equivalent SSB signal
The signal is S3 (weak signals)
The signal-to-noise ratio is equivalent to +3dB in a 2.5 kHz bandwidth✓Correct answer
The signal is 3 dB over S9
Explanation
WSJT-X reports signal-to-noise ratio normalized to a standard 2500 Hz reference bandwidth so that reports are comparable regardless of the decoder's actual bandwidth. It is a signal-to-noise figure, not an S-meter reading.