I don't know that there's much special about that first picture that you posted.
But usually when you see this type of symbol...
Originally Posted by Austins1hobby
... it's a Nautical Star. Reportedly, it was traditionally worn by those in the Navy or Marine Corps, or sailors that made their living on or near the sea. A red and green star on the port and starboard sides of the chest, respectively, had a special significance.
There are only a couple of gang associations that I could find. The Russian mafia might put a star on each shoulder of a "made-man", and there are some gangs in northern california that use a variation of the star as a symbol (the Nor-Cal Star; I think it was supposed to be the mirror image of the Nautical Star, i.e. black on the opposite side of the arms, but it almost seems like they're interchangeable now; in the picture above, the girl would be wearing a Nautical Star on her left, and a Nor-cal Star on her right).
Personally, I'd think that it started out having and probably still has some special meaning to some people (guidance, finding their way home, etc.), and then others saw it just as a neat symbol that looks cool and it evolved into a bit of a trend. I'd be surprised if it indicated any sort of gang or other kind of organizational involvement around here.
Here's some more info:
http://en.wikipedia.org/wiki/Nautical_star
http://www.tattoo.com/blog/nautical-...t-does-it-mean