We have several birds. Each one defends it's territory differently. Many signs of the bird being territorial take large amounts of time to understand. They can often be confused with playfullness, excitement, jealousy, or not feeling well.
One: thing I always look for is pinning of the eyes. Most of us know this term, but for those of you who don't, it's when the eyes dialate and contract at a very rapid rate. Our M2 (Moluccan Cockatoo) is harder to judge with this, as his pupils and eyes are very dark. Our macaw, is very easy to see this.
Second: thing is "blushing". This really only applies to macaws. There are exceptions to the rule, but for now we'll leave it at this. Whether it be a Blue and Gold, Military, Severe, Hahns, etc, etc....they will blush. This can mean they are stimulated, jealous, or you'd better move quick.
Third: thing is body language. When a bird opens his crest and wings and broadens his stance, lunges, blushes (Macaws only), and eyes start pinning...you're gonna get bit! Make no mistake about it, there is something they don't like. Our B&G does this if I wear a hat. Our M2 does this if you wear glasses. Our quaker does it if you are near his cage and he doesn't know you.
He's really upset in this pic. I purposely put my hat on to demonstrate
Fourth: thing is feathers. LOL, birds can move their feathers like you or I do our eyebrows. Cockatoos use their crests and wings as a sign of "I'm bigger than you". Our B&G will raise up two sides of his head feathers. I call these the horns of doom. See the pics below!
I had my glasses on...see, he doesn't like those!
See how each side of his head feathers are up?
This is not to be confused with a happy bird.....when they're happy, they will raise ALL their feathers. Giant blue q-tips
On the subject of feathers, birds will sometimes tag you from behind, or when you're not looking

They do this in their flocks in nature too. If one large parrot does not like another.....or.....the other has offended in some way. When they turn their backs they will pluck tail feathers out. It's like you telling someone to go to hell. Same thing for them.
Sorry for jacking your thread, but maybe someone can get some useful info here. The first pic is my boy....love him to death and have the scars to prove it

. He will do the same thing around his cage or if he doesn't know you. Our M2 doesn't bite, he will let you know with his body if he disapproves of something, but once you figure it out....you'd better be ready to be smothered in love
