There are different types of Police in Mexico; Federal, State, Municipal and Tourist. If you are around town and something happens, you’ll probably be dealing with the Municipal police. They can be found in the center of Tulum. The tourist police are there to help tourists deal with lost property and the likes. The Federal police deal with larger federal matters and you shouldn’t see any transit police unless you’re driving.
Keep an alternative contact with you for someone to call if you get into trouble, be it a travel partner, someone in the hotel or hostel where you are staying
Generally speaking, the police in Mexico are a forgiving and nice bunch of people that are here to ensure everyone has a good time. You will see them about, some look very intimidating with heavy machine guns, be polite say hello and enjoy Mexico. They’re here for your safety.