If a country has a pattern of tourists being targeted by criminals on public transport, that information is mentioned in the Country Specific Information in the section about crime.
Taxis. Only take taxis clearly identified with official markings. Beware of unmarked cabs.
Trains. Well-organized, systematic robbery of passengers on trains along popular tourists routes is a problem. It is more common at night and especially on overnight trains.
If you see your way being blocked by a stranger and another person is very close to you from behind, move away. This can happen in the corridor of the train or on the platform or station.
Do not accept food or drink from strangers. Criminals have been known to drug food or drink offered to passengers. Criminals may also spray sleeping gas in train compartments. Where possible, lock your compartment. If it cannot be locked securely, take turns sleeping in shifts with your traveling companions. If that is not possible, stay awake. If you must sleep unprotected, tie down your luggage and secure your valuables to the extent possible.
Do not be afraid to alert authorities if you feel threatened...