In an auditorium the announcer asks the audience to be seated on the left side seats. Doesnt it mean the left side of the audience??
In such circumstances, it is safe to assume that the announcer means the left side from the perspective of the audience. If the announcer does in fact mean their own left side, then they are not a very good announcer. The same situation arises in things like exercise classes. In such cases, the public speakers should (and usually do) make directional references from the audience's perspective.