Creep Workaround Issue:
In later versions of Sierra, there is a current bug that applies lines to the spine of a layout when creep is applied. When the checkbox "Align the marks to the outermost signature when setting the creep" and apply "Signature Registration Marks" or "Signature Trim Marks" to a saddle stitch or perfect bound job with multiple impositions on the sheet, then the additional imposition gets lines on the spine of the layout.
Turn off the Signature Registration Marks and Signature Trim Marks in the Dynamic Marks tab that's applied to the additional impositions on the sheet.
With "Signature Centre Register Mark’ turned on the line appears.