One of the protesters, Chris Howson, told the Newham Recorder that arms fairs like this one were "fuelling the wars of tomorrow".
He said: "We are here to pray for peace because most people have no idea that they are selling weapons that can be used to kill women and children.”
More top news
Police have stepped up patrols after a woman in her 40s was "dragged to the ground" in a park in east London.
Families living near Heathrow say they are supporting a group of activists facing jail for chaining themselves to the airport's runway.
Police were called to break up a "large fight" which involved a baseball bat, a man dislocating his shoulder and three arrests.