How does one "prove" to be Muslim to enter Mecca?

I know that only Muslims are allowed to enter mecca. But I've tried searching, maybe I couldn't find it or there's not much to find about it. So how does one prove if one is Muslim or not? Sure one could say by traditions, the way they act... but there are Muslims all over the world, some more devout than others, just like there are non-Muslims who know more about Islam or know nothing about it. So really how would and how does the government and all ensure that only Muslims enter mecca? For all we know, secretly dozens, maybe even hundreds of non-Muslims are entering it every year. I'd appreciate an answer with a proper explanation. On an earlier post explaining only Muslims can enter someone mentioned not to get caught by the police. So what would the police do? check your papers? IS there a doent proving one is Muslim?