I don't want to say "non-explicit" or "innocuous" or "inoffensive"--I want each rating to be what the content is, not what it is not. And it's hard to come up with positive, rather than negative, labels for the default assumptions. I've had some interesting linguistic realizations, trying to choose these labels.
I also like that "worksafe" doesn't imply "juvenile and simplistic," and I had a hard time finding words that meant "no offensive content" but didn't imply puerile, shallow, or trivial.
That said, I'm not enamoured of "worksafe;" I just couldn't find another word that fit the meaning I want the label to encompass.