Karen, pinching will not produce a Y. Here is a link to a page I made about the Brugmansia Y - it also shows other indicators of blooming:
http://www.xeramtheum.com/myst...
Also, for those of you who have them in the ground, once a frost knocks them down do NOT cut them back unless you are absolutely 120% sure that the branch is completely dead. Otherwise you risk having the roots send out new shoots which will be definitely killed during the next freeze. When I was growing them in the ground I'd cut the dead branches back around March.