In the chestburster sequence continuity is all over the place? a science pin can be glimpsed on Kane's buckle first, then the navigators pin and then a change to the executive insignia pin?
They either produced divisional buckles for all the crew and decided that if everybody had them it would look a little too Star Trek? or the original pin fell off (lousy glue) like the insignia pins on the uniforms? and whoever replaced the pin amidst all the mess and confusion didn't notice the difference? that along with the uniform patches changing colour in that scene?
So kane starts thrashing about wearing the blue science division pin on his buckle, then at the next cut as the blood first appears on his shirt he's now wearing the navigators insignia, and on the final cut as the chestburster is emerging it's now changed to his correct executive pin? Seeing as they were constantly changing the actor's bloody shirts, inbetween setups, and the outfit on the Kane false torso it's not surprising these minor discrepancies occurred.
These are the unidentified white plastic doodads, certainly look similar to windows used for model railway buildings? (thanks to stephen210)