What is the meaning of -//- sign?
Unlike P and O sequences which are literally joined at their ends, the sequences trpR and P are rather distant. The DNA between them is so long, that the limited space of the page prevents a decent proportional representation. So instead of painting a long line of limited-importance strands, the graphic designer choose to omit the part between slashes.

Note that despite the apparent disconnect possibly suggested by the sign -//-, the intervening DNA is continuous. The sequences trpR and P are still on the same chromosome.