It's hard to distinguish your current level of intelligence with all the stuff you've learned. Knowing what I know now I'd probably go for tapping prime number sequences on the glass, but it took millenia of humans that were basically as intelligent as me to figure out that prime numbers are interesting.
That is true. I was thinking that morse code or writing would be effective, but my knowledge of these things is not really intelligence but rather things that I learned by participating in human society.
