Final answer:
The + symbol on a railway timetable typically denotes an interlocking, a safety mechanism that prevents conflicting train movements on a track layout.
Step-by-step explanation:
The + symbol in a timetable usually indicates an interlocking. An interlocking is a railway signal apparatus that prevents conflicting movements through an arrangement of tracks such as junctions or crossings. It is a safety measure to ensure that only one train moves in a particular area at a time, preventing accidents. The plus sign could be a note to refer to a particular condition or rule regarding the interlocking that might be further explained in a footnote found elsewhere in the timetable document. This notation is part of the detailed and complex language of railway operations.