Agreed that the center of galaxy is the best place to put up a billboard. Ha, what if that's all it was, an advert, "Be Sure To Drink Your Ovaltine." Galactic trolls, ha.

Is the signal's data available publicly? I wonder what the cryptanalyst community would think of it.

I would think that a intelligent species capable of placing a galactic billboard at the center of the galaxy would be intelligent enough to encode their message in an easy to decipher manner. Although, what does "easy to decipher" mean to a species with that technology. They may have stopped using any form of language that we would understand, generations ago.

Is math a universal language? Could an alien species use a number system that we wouldn't recognize?