When we wrote simple mathematics on the Pioneer and Voyager probes I think it was under the assumption that anyone or anything else finding them would have co-discovered enough mathematics to recognize it on the plaques. That's the sense in which I use the word "discovered" for much of mathematics. Our definitions will differ from aliens but the foundations will be translatable.
On a side note, and since you mentioned Roman Numerals in your other comment, I would say that the representation of I, II and III being different from IV is related to how the human brain processes quantities up to 4 [0].
So it is a simple example showing that the way humans process language influences the representation/definition of mathematical ideas.
