A metaphorical stick used to "hit" a person in an effort to remedy that person's ignorance or incompetence.
Get the clue stick, quick! ... Did you see the recent Openlaw coverage, in which ideas for arguments in defense of the DeCSS defendants are being collected online, so that anyone can contribute? ... What earthly benefit could a legal team gain in building a case in full view of the opposing side?"
J. S. Kelly, "Open source: It's the law," LinuxWorld, March 2000
"Why does the media continue to insist that Linux is 'no good for the desktop'? What needs to be done to stop this pervading image from persisting? Time, and repeated whacks upside the head with a clue stick!"
Peter Collinson, "The work of Eric S. Raymond," EXE, April 1, 1999
If a person is ignorant or incompetent, we say that person doesn't have a clue or is clueless. We fantasize about knocking some sense into the person, and a clue stick seems like the ideal tool for the job.
This phrase dates to 1993 in Usenet newsgroups (thanks John Drummond for unearthing the earliest use).
A similar implement is a clue-by-four (rhymes with two-by-four), a phrase often seen in newsgroups, mailing lists, and other online locales, but which has never (at least to my knowledge) made the leap to the offline media. (Note, too, that the trademarked term Clue-by-Four™ refers to, as the U.S. Trademark Office says, "a novelty toy, namely a foam rubber two-by-four shaped board.")
Another popular variation on this theme is clue train (or cluetrain), a metaphorical train on which an ignorant or incompetent person needs to ride. This phrase was popularized a couple of years ago by the publication of The Cluetrain Manifesto on the Web (see http://www.cluetrain.com/) and in book form. Here's the earliest citation I could find, which also provides a few other suggestions for helping a person get a clue:
"The Top 10 things to say to the terminally clueless:
10. Step into the rain and let a few clue drops hit you.
9. Go to a restaurant and order something off the clue menu.
8. Open up a book and read a clue chapter.
7. Step on the elevator and get off at the clue floor.
6. Pick up the clue phone.
5. Buy a ticket on the clue train.
4. Hit the road and go to the clue outlet mall.
3. Take a dip in the clue end of the pool.
2. Make like a detective and find a clue.
1. Take a hike in the clue forest."
"Send a movie executive to clue camp," The Orlando Sentinel, October 21, 1994