>>> MISSING
<class '__main__.MISSING'>

I think a repr of just "MISSING", or maybe "dataclasses.MISSING" would be better.

I literally just went down this road--for a while there was a special sentinel value for the eval_str parameter to inspect.get_annotations().  The repr I went with was "<id>", e.g "<MISSING>".  It depends on how seriously you take the idea that eval(repr(x)) == x.  Certainly most objects don't actually support that, e.g., uh, object(), a type which I understand is available in most Python implementations.

Cheers,

/arry