No. Why would you?
If you plan on posting an answer immediately, then the warning is redundant: they can see that you self-answered.
If you plan on sitting around and watching for other answers before posting your own, then the warning is counter-productive: you may not get any good answers if you imply that you've already made up your mind as to what the answer is.
And if you don't plan on answering, but then find the answer after asking the question, it's too late for a warning anyway, as folks may have already written answers, or be in the process of writing them.
The only thing I'd caution you about would be waiting until someone's already written an answer roughly equivalent to yours, and then posting your own. First off, there's no need for it at that point... but also, it can seem to the author that you're trying to cheat him out of up-votes after he took the time to answer you. If you have an answer prepared, either post it immediately after the question, or post it only if no one else provides a similar answer.