Agree with 芝達 & WaWaMom. Since your BB is 14months, and can start with him about what's right and what's wrong and 講道理, so you can tell him that screaming is no good and incorrect, and teach him a correct method to catch your attention or tell him the appropriate expression. Then, after a certain period of time, situation will improve.
My son is currently 3year-old, and he used to shout when I talked with others or when he wanted to catch my attention, then when I told him that I'd like him to inform me & count until 10 to draw my attention, and insisted for several weeks, now he will say "mami, I'd like to talk with you" instead of just shouting.
I totally agree that BB at that age screams a lot because they cannot yet express themselves in words easily. My son is nearly 14 months old and he started screaming a lot a few weeks ago. I find that he will stop screaming once we can successfully guess what he wants. After hearing the advices from other moms, I think we may try this everytime our BB screams again: Calm ourselves down first, don't get irritated once they start screaming, esp in public places. Then we should try to let them know that we will find out what they want and start making guesses until we can get it. We should even try to attend to them once we know they are trying to tell us smth, before they start screaming. Don't make them feel that they need to scream to catch our attention. I think even they cannot talk very well yet, they are able to understand us.
Don't give up, I strongly believe that our reactions to them now are very important to the development of their behaviour.