What is the significance of the 'crescent moon-star' symbol seen on flags and ancient drawings?

On April 23, 1998 there was a similar conjunction with Venus and Jupiter within 1 degree of a crescent moon. These kinds of conjunctions between the crescent moon and a bright planet like Venus or Jupiter are not that rare, but are very spectacular!

Even more interesting is that around 1054 AD, a supernova in the constellation Taurus, which produced the famous 'Crab Nebula', may also have been the most spectacular during the time of a crescent moon phase. Some north american indian petroglyphs show a crescent and a bright star together, and this event must have been simply dazzling, not to mention the many possible mythological/religious interpretations of this 'sign'.