I thought all those fancy-pants OLED displays had the same or better software than the IPS “super” LCD displays on the cheaper models. On my SJ8500, to access the meter:
(LG webOS version 05.80.15)
All Settings > Channel Tuning > Manual Tuning > Antenna DTV > Channel Number (select the actual channel from a pop up menu or scroll up or down with the channel selector on the remote, not the virtual or sub-channel).
There are two on screen display bars- “Signal Strength” and “Signal Quality” that display as a bar graph with a numeric percentage value (there’s no reference, so it’s unknown if that’s dBm, dB, whatever- so the readout isn’t easily related to that from another device). If you move the antenna, or multi path conditions exist, the Strength Meter will move.