Random thought: if you have to put a cliffhanger warning on your book, you're likely doing it wrong.
Cliffhangers can be good things if done well, but warning your audience that the book has a cliffhanger does NOT help your case if you use one, especially since it may draw attention to the nature of the ending before the reader even picks up the book. And that kills anticipation.
I usually think its a better idea that if you're uncomfortable with writing a cliffhanger, don't use one. Try to make it a self-contained story with lingering threads to keep the anticipation going. Or try different endings and see how they read before opting for the cliff, especially if you're new to doing it. My rant for the day, especially since I saw more than a few galleys on NG saying "Cliffhanger warning" - that drove me up the wall so badly. I'm likely still going to read those books though.