I think that "Alignment Curve Return" is just a type of alignment, not an object.
Actually, is the same that any another Aligment.
Alignment Class has the property Type, when you can choose what type do you want.
One of this types is just "Alignment Curve Return".

You can Read/write this property.
Then, according to the choosen type, the alignment will appear in the ToolSpace, within the Alignment category, in the specific type folder.
By default, when you create an automatic Intersection or Roundabout, all involved new alignments will have this type.
I think that it just serves to differ the alignments in several folders in the ToolSpace.
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