I haven't seen a lot more traffic on this idea, so below I've posted some of the ideas generated and a repeat of the original stipulations. For those that missed the earlier post, I'm interested in a Universal Symbol that those who have read of the horrific knowledge of HPL might use to identify themselves to others in the clan. It also has no meaning to anyone outside of the know. I like this because it's short, and although I haven't seen the Arabic rendering, I presume it to be stylistic. Secret Service agents who also read Arabic, and understand it to be a secret sign for a completely different type of organization.
Terror overcomes All.