Gamer's Hell has conducted an interview with NCsoft's Richard Garriott, quizzing the Ultima creator about the Logos language he created for Tabula Rasa.
Q: How does the Logos language differ from the runic language you created for UO?
A: In Ultima, I used a (runic) language that was sourced in the same way Tolkien sourced his runes for the Lord of the Rings. If you look up runes in any encyclopedia, you will find similar runes that were the forerunners of the Roman alphabet. Runes work great for English speaking westerners, as they are an easy letter for letter substitution of similar letters and can be used to hide words in a simple-to-decipher code.
For Tabula Rasa I had very different needs. While I still wanted it to be easily decipherable, I needed for that to be true regardless of your country of origin and spoken language. Thus I chose to create a (logogrammatic) language. The result also works fictionally. In Tabula Rasa fiction the advanced aliens that left a message throughout the universe would also likely use a pictographic language to make their messages easy to read by all civilizations that advanced far enough to develop language skills.