I believe the original intent was mostly about reporting unattended bags that could contain bombs, not reporting your neighbor for hosting a socialist book club or whatever. Obviously it's vague and broad enough that it could be bent to more sinister purposes though.
Perhaps a slightly different context but I have heard this almost verbatim a few days ago on buses and trains in Birmingham, UK.
If I'm not mistaken too, I believe that "If you have nothing to hide, you have nothing to fear" is also something the Govt used a few years ago.
http://www.btp.police.uk/latest_news/see_it_say_it_sorted_ne...
The content of the ad includes someone looking at someones trash, seeing some common chemicals and assuming they are making a bomb.