Yeah - if you put your turn signal on, it's like telling the other team what play you're about to run. Their defense will be ready before you can move the wheel!
You'll even get people BEHIND you change lanes (into the one you wanted to change to) in order to pass you b/c they think you're an idiot. Oh, and no way are they going to let you in either! So it compounds the problem.
I like to use my signal once I'm halfway in the other lane, or at the very last second when I'm already over the line. This way they know they've just been served. I'm not some driver who drifted out of his lane - I did it on purpose!
Best way to change lanes is to almost hit the rear bumper of the car next to you. Once you complete the lane change, you should be about 2-3' off their bumper! (that's the 1 car length rule - gives people a space to jump in!) After you're in the lane, you can slow down and give it 10' off the other guy's bumper.
With time and practice, you can tell exactly *who* is about to change lanes and when!
On a related note - I'm going to order some Hella Supertones for my daily driver. These are very loud horns that put out about 118db of sound. As a comparison, that would make them 7x louder than a standard horn! Think ambulance horn volume. Yeah - that's what I'm talking about! If someone makes me use my horn, I'll be sure they need to change their shorts afterwards! hehehe
'68 Firebird, 350-4, 2 spd auto, triple black, Dlx Interior