So I read this thread this morning and while I waited for my son to finish up soccer practice, I debated about pulling out my brand new 2017 MacBook in space gray and inspecting it. I thought for a second - should I look for this, as it's something I've not noticed, but what if it's there? My OCD would surely win this debate.
I pulled it out of it's new pleather case and, sure as ****, there was a circle around the logo and it can only be seen when held up to daylight at just the right angle. I smeared my finger (and some spit) around the line and it seemed to go away. After getting home I wiped it down with a damp paper towel with a drop of liquid dishwashing soap. This provided a similar level of friction as my finger. The marks were completely gone and the surface was spotless.
This experience reminds me of the Proto Armour for Raspberry Pi cases we make at work (
www.protoarmour.com). They are machined out of aluminum and tumble finished, and some are anodized in various colors. So the thing with tumble or bead-blasted aluminum with darker anodized finishes is that when they pick up residue from fingers, or low-adhesion decals (i.e. Apple logo protector during manufacture, etc.), it's more noticeable than with lighter colored finishes (i.e. clear anodized aluminum).
I guess what is important is don't panic, this is something that can be fixed without much fuss. I can't say the OP didn't have a more severe issue with a material handler having too much suction during manufacture, not impossible, but it would be the first case I've heard of in dozens of MacBooks I've owned over the years. Here's to hoping such issues don't happen often.