If you go to 1:44:35 in the movie you will see that ontop of the pole that Indiana and Marion are tied to a pole, on top of the pole you will notice the head of R2D2.
What you see in this scene may appear to be R2D2's head, but it is not. If you look at the other flood lights in the moments before the Ark is opened you will find that what looks like R2's head is actually just the shade to direct light for the flood lights. The what looks like the markings on R2's head is actually the openings in the back of the shades most likely for heat dispursement. The light bulb on the light post that Indy and Marion are tied to is not on. If it was you'd never think that it looked like anything other than a shade.
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