humanity would see the triangular shape and begin to trace the three origin points through space, based on its rotation, to possibly discover something of great wonder.
Just noting that this is even more improbable than aliens putting the "pyramid" there. If you tried to calculate previous locations and orientations of the comet, the measurement and calculation errors would accumulate, and in the end the orientation of the pyramid (and whatever these "origin" points are) would come back as if written in gibberish. There's a reason why you use GPS for navigation, not the internal accelerometer of your phone, which could theoretically determine your location without external sources.