adobe-illustrator

I am reading into Illustrator a PDF output from R (grid graphics I believe) in which the circles show as boxes with crosses inside them. These pictures illustrate:

Let’s say I have a shape that I rotated at an awkward angle of let’s say 34°. I close the document, return a few hours later, and want to straighten the it back to its original 90° or 0° angle. The problem is I don’t remember the angle I originally rotated it at. Shift + Rotating nor resetting its bounding box does the trick. Any shortcuts/options I’m overlooking here? For example how would I rotate this quadrilateral so that it sits horizontally straight and looks like a box.