At the end, wayfinding is best when it is present only where you need information and gives you only that essential information you need to make your decision (where to go, where you are).
For example, if you arrive in an underground station, looking forward to reach your destination a sign should show you the directions where you can find the bus stops connecting the station, the tramps or the exit whether there are different exits and directions. The next decision you might have to take is from where your bus line departs.
Signage has to be simple and easy to understand with a high contrast and common symbols and should function with or without colours. Wayfinding information should be given on a base of at least two way communication channels (visual, audio or sense), so perception is higher in general and people with disabilities are integrated. Symbols should use colours, but they should work without them in order to provide information for colour blind people.
All symbols should look the same and should be used throughout the city. For ease of use, this should include not only common symbols for means of transport but moving stairs, elevators and information for mobility restricted users and general attractions.
A simple signage that is easy-to-understand commonly used and constructive for the customer is hard to implement. The ease of use for the user is facing a major challenge in general to gain a good wayfinding. It requires many stakeholders working together especially if they will be integrated, beyond Public Transport operation, in all kind of signage and communication of the city. On the other hand, any change requires big budgets, because it is related to infrastructure and needs to be done throughout the whole network and in all vehicles in similar quality to be reliable.
On a more elaborated level, the upcoming availability of smart phones and mobile internet gives a wide set of opportunities for navigation on the surface, while indoor and underground navigation is still limited, but in reach and already piloted.