Hard if not impossible to tell from the cabin.
If you are on a McDonald Douglas MD-80 series jet, and you are sitting up in first class (further back, and you have exceptional hearing) and after touchdown sometime during the deceleration phase on the runway hear an automated warbling warning sound followed by a female voice saying “autopilot disconnect” then you can surmise you just experienced an autoland. Those autopilot disconnect sounds are audible to me when I am sitting in the front. Otherwise, unless the flight crew informs you of their intentions to autloand, there would not be any noticeable difference during the flight phase.
Additionally if it is exceedingly foggy with very limited visibility around the airport you can be pretty sure that the only way for airplanes to land would be to use some sort of autoland capability.
The 737NG that I now fly has a HUD (Heads Up Display) that allows me to “hand fly” (no autopilot) down to the same low visibility minimums as I could using the jet’s autopilot coupled autoland capability.