What does the Red Crescent symbol stand for?

Answer 1

Answer

Short Answer:  The Red Crescent is an internationally accepted symbol that stands for emergency assistance, and is simply another symbol for the commonly known Red Cross.  In fact, the full name of the "Red Cross" is "International Federation of Red Cross and Red Crescent Societies"

Longer Answer:  Soon after the formation of the Red Cross in 1864, the cause was warmly accepted by Turkey, however due to objections that the Red Cross symbol could be viewed in as a religious symbol, the Red Crescent was instead used as an alternative.  It wasn't until 1929 that the Crescent was official recognized, which was fortunate as the Red Crescent's activities in Greece saved countless lives during World War Two.

Other countries have their own variants of the symbols with different histories behind them.  Iran for example was authorized in the use of a Red Lion and Sun symbol, however it has fallen out of use since the 1980's.  Israel has pushed for recognition of the Red Star of David.  The Red Cross felt the increasing number of symbols was both distracting from the goal of the organization and a point of hazard in that less-known symbols could be misunderstood and result in injury or death.  

In 2005, to settle these disagreements, the Red Cross adopted the Red Crystal Symbol for use during international aid.  Individual groups were to place a small version of their respective symbols within a large Red Crystal shape which allows for simple visual verification, but still allows the use of various protected symbols.

Longest Answer:  There are dozens of books on the history of the Red Cross detailing an amazing history.  

Start with "The Red Cross in peace and war By Clara Barton" for an early history, then "The humanitarians: the International Committee of the Red Cross By David P. Forsythe" for a more recent view.