Is there any indication to the crew of the aircraft about any potential leakage of fuel from any part of the plane?
In a typical trainer aircraft (in this case, a C172), you have an annunciator panel that includes a "Low Fuel" light:
These lights only come on when fuel is low if the lights are functioning properly. This panel is located prominently, and is easy to notice. This is only one aircraft, but when you consider it is an entry level aircraft that is less sophisticated, it gives a baseline idea of what you could expect to see.
Also, there are fuel gauges displayed with all engine instruments that will indicate accordingly. While this isn't a leak detector, pilots are trained to monitor all instruments regularly and cross check the values - which is how a leak is identified in aircraft with low amounts of technology.
It is worth noting that checking the "LOW FUEL" annunciator is off is a regular checklist item that occurs before you start your actual flight.
As GdD mentions in the comments - you are taught not to rely on any one instrument indication, and panel lights are no exception.
There is no special indicator or warning about a fuel leak because it would be difficult to automatically detect a fuel leak with any certainty (fuel flow sensors are not super accurate, nor are fuel quantity sensors).
Pilots of small, single tank airplanes must rely on reading the fuel quantity indicators periodically and "knowing" how much fuel should be left and how much is actually left. Big discrepancies indicate a possible fuel leak.
Pilots of bigger, multi-tank airplanes check for (and, on more sophisticated airplanes, are warned about) fuel imbalances between tanks. A fuel imbalance again, indicates a fuel leak as it is very very unlikely that the same quantity has leaked from both tanks.
You can find further info about fuel leak detection on Airbus airplanes here.