One of the things I noticed when looking over social concern posters was that they often rely upon images and symbols that we recognize and are familiar with, they then twist those images to mean something else, to bring awareness. You want to cause the viewer to question what you have said, to make them think about it carefully and then be driven to action.
There are a number of ways one can go about bringing awareness to their cause. It can be through shock factor, humour, powerful photographs, or even through offending others (though this is not always the best approach, and must be thought through carefully).
Another this is that you must make sure that you really fully understand what you are representing, that means knowing more than the surface level and taking the time to figure out what the arguments for your concern are and also the arguments of those who may oppose what you are trying to bring awareness to. Further, it is also always important to have a clear idea of who your audience is, who are you trying to reach because that can greatly impact the design and style of your poster.
The posters I have chosen as examples this time use everyday objects and stuff we see all the time to bring awareness to bring about social concern. I really like the first poster which uses the baggage tag for luggage to remind us how human trafficking. The second one is an international advertisement for concerns over fast food and the negative impact it can have upon your health. And the final one against uses a piano without its black keys to grab our attention and bring awareness to the issue of racism.