Mr. Rewrite is embarrassed to admit that if you search this site for the term hmmm you'll find at least three uses in that format. When it finally came up in an edit recently, he finally thought to look it up.
Alert the media: Mr. Rewrite was wrong. It happens occasionally and sometimes spectacularly, as in this case. It involves one of Mr. Rewrite's favorite snarky terms.
Webster's New World College Dictionary, Fourth Edition, where The Associated Press turn for matters not covered by its stylebook, has an entry calling or hmm.
Hmm. Mr. Rewrite wonders how many times he's botched this term over the years. Too many to count, he thinks.