When in cities, be ready for strangers who will approach, tell a tale of woe, and then request several dollars. In the majority of cases the tale is a scam, so do not feel any obligation to part with your cash. Some cities have a particular problem with aggressive panhandlers asking for money. In any case the best procedure is to firmly say "No" and walk away.
Two occasions during which visitors should be particularly cautious are while driving and when being approached in cities. When driving, do not let anyone in your car you don't know; if anyone reaches for your car's doorhandle, drive away immediately. In cities it is best to keep the car doors locked and the windows up, especially at night. Always keep personal belongings in the trunk of your car, out of view of curious passersby. Picking up hitchhikers is generally considered to be unsafe, and is illegal in some states.
Street drugs, including marijuana, are illegal in all 50 states. Prostitution is illegal in all areas except at brothels in rural Nevada counties. American police make wide use of the "sting" operation, in which a police officer may pose as, say, a drug dealer or a prostitute in order to catch and arrest persons intending to buy or sell such services.
Most Americans frown upon illicit drug use regardless of quantity and travelers would be wise to avoid bringing or using such substances in the United States. Tolerance for prostitution varies by locale and the form it takes. Engaging the services of a street prostitute puts one at a very high risk of sexually transmitted diseases, an embarrassing arrest, and/or being robbed.
During any emergency, dialing 911 at any telephone will connect you to an area call center for all the emergency services in the area (police, fire, ambulance, etc.). Calls to 911 are free from payphones. Dispatchers will send appropriate personnel to deal with accidents, serious sickness, criminal or any other emergency situations. Unless you are calling from a mobile phone, the 911 call center can almost always trace your call to locate the caller. Abuse of the 911 program for non-emergency purposes can result in a heavy fine; only use this service for true emergencies. Some cities have a 311 number for situations which are not of immediate danger.