I think this should not be embedded into function names.
My Idea:
Arc IDEs could instead manage attributes for names like "predicate", "has side effects", or "is a global".
IDEs would search for such tags in the docstring of a function and syntax-highlight it accordingly.
Lisp does not have enough syntax to highlight anyway.
And I completely concur (great word choice)--I'm working in a text editor right now (TextMate, not Emacs), and it's perfectly suitable. Forcing use of an IDE, or biasing towards it, would turn me away from the language.