A sign!

I finished my exams, and I went on a walk-about. All sort of adventures and interesting things including trespassing onto Malaysian land(come to think of it, it's kind of suspicious). Anyway, this sign which I saw. 2 sentences which by themselves are meaningful and usual. It's just kindof strange when they are put together.

If it's monitored by cameras, why do you need us to call the police if there is anything suspicious?
And we should call the police in cases of suspicious activities because the place is important enought to be monitored by security cameras which are nevertheless prone to failure during periods of suspicious activities and must rely on civil minded citizens who happens to walk past to call the police.