Does anyone know how I might get this off?

[eraser]

It looks like paint.  I hope that there is some way I can remove it without ruining the case plastic.

 

[jessenator]

Goof Off? Any orange-oil-based solvent that is plastic/polymer safe might be safe.

 

[Unknown_K]

As far as unwanted markings go that looks professional and not too bad so I would leave it.

If it is really bothering you take an exacto knife and remove one small portion to see if it is paint or a sticker and then try different solvents to see what dissolved it without risking the case.

Be aware that is that marking has been on the unit a long time and the case has discolored at all then removing the marking will still show a shadow in the plastics because it blocked sunlight from discoloring the plastic underneath.

 

[omidimo]

Try Goo-Gone first, it is gentler than Goo-off. 

 

[unity]

Brake fluid. I know some people have used it with great success. I seem to recall a black painted Lisa getting cleaned up that way.

 

[eraser]

Thanks guys.  I will experiment on a small section.  I expect to retrobrite this Mac as it is because of needing to replace the faceplate too and the color doesn't exactly match.  So I will get the case one uniform color one way or another.