Pictograms are still a written language. Also, 30 is hardly a pictogram nor is !, &, checkmark, or a + symbol these are also only meaningful because you have seen those symbols before.

Plenty of others like thumbs up sign are culturally dependent. EX: You see someone doing a thumbs up, but their biting the thumb what does that mean?

PS: It's still an interesting exercise IMO because people recognize a much wider symbolic language than they generally think about.