If you posted your answer, somebody is bound to see it. There isn't much of a point announcing your answer, it just creates a needless distraction before someone even gets a chance to see your answer, and at worst it'll even discourage someone from looking at your answer (for reasons like what Da_smokes said, they smell like rep-whoring).
You can flag such comments as not constructive or too chatty.
I do post such a comment if I think I have a good reason to call attention to my answer, for instance if I believe the existing answers are misleading or wrong despite having received upvotes:
Note that many of the answers here miss a certain important point [explain what that point is], which I've addressed in an answer of my own.
but that doesn't mean if I don't comment, nobody will see my answer.
At the end of the day, it's all about whether a comment adds any useful information to the topic at hand. If it doesn't, it's noise and it doesn't need to be there.