I love the little green aliens in Mr. Wuffles, with their long, flowy robes in Star Trek coded colours.
Here you can read some fantastic insight into how David Wiesner created the alien language.
He started from geometric symbols, which gives the general idea of aliens thinking ideographically, then selected fixed clusters of them by using a Cardan grill, which suggests syntactic structure, and finally added fractions, which remarks that they’re aliens, we may share some geometry, ideographic and syntactic phrasing, but there will still be something strange, something we can grasp but not fully understand about them. Also the recurring exclamation mark suggests emotion but who can say, it’s sweet touch.
I think this is a brilliant process to design asemic writing.