In Iron Man the movie, Mr. Stark said:
I am Iron Man.
to reveal his concealed identity.
In which case, the sentence was used to identify who he is. (specifying use)
Now, if he was trying to brag about how "great" he is, as is often the case, could he be saying the same sentence to those who already know he's Iron Man? (ascriptive use)
I am Iron Man. And you know I can do things that you can never imagine.
In case my question above is not clear to you, I was asking whether "I am Iron Man." in the latter example does not identify who he is but ascribes the property of "Iron Man" to the subject "I".