Nero ShowTime is the only DVD player I know to show the layer number being played.
But, as there is more than one way to declare the layer break in the video_ts.ifo, with some DVDs ShowTime gets confused: it keeps showing layer=bottom even after the layer change, and it only refreshes this data after a chapter change, or after manually advancing with the cursor.
I will be grateful if somebody tells me about a different player that displays the layer onscreen. Windows Media, PowerDVD, uLead, Media Player Classic, etc. don't.