M.S.
Most importantly, who cares who is watching! Sorry, but it doesn't matter!
Your 8mos old isn't talking yet. He is trying to communicate. The best things you can do to help minimize the screaming is to not put him in a situation where he may scream - going out tired/hungry/etc.. teach him to sign if you aren't already. Otherwise, big deal. The more attention you draw to it, the worse it will be. Rather than focus on the people around you that are watching, focus just on him and make it your one and only job in that moment to find out what is bothering him.
Good news is this way of communicating will pass and you can help him be a better communicator at 2, 3 and so on by listening to him now and anticipating his needs/wants.
M.