i seem to remember, not long ago some body requesting info about lines on the carpet, wondering if they where filtration marks,
At the time i said mike halliday had posted an excellent example of some caused by carpet fitters gripper, along with marks from a ," I believe plant pot" well as mike had couldnt upload , or find , here is the pic,
found them hidden away in one of my folders mike , hope you dont mind me posting,