This is a dirty little trick to create a zig-zag stroke in InDesign - as you may know, such a stroke style does not exist in the application.
The idea is to use two overlapping lines with Right and Left Slant Dash strokes applied:
Offset one of the lines to get the zig-zag shape. Use the X position to precisely position the lines and finally add a rectangle above them.
Unfortunately this is not a universal solution so I don’t recommend using it in production. You would better find other ways (e.g. a placed Illustrator artwork) but for very simple projects it can be an option.