Well, a 'G' is often found in certain types of music, for example the song "Nuthin' but a G thang" on Dr. Dre's seminal 1992 album 'The Chronic'. In modern rap parlance a 'G' stands for any word really that begins with that letter, eg God, Girl etc but most often it stands for "gangsta". It can also mean money, for example in the lyric "I clock G's while you clock Z's" (2Pac? not sure).
Round these parts I've seen it most often at the end of genius' posts, where I've taken it to stand for "genius", but mebbe he and others are suggesting that they are gangstas, God, or perhaps advocates of the type of music called "G-Funk", usually associated with such artists as Warren G and Nate Dogg. Unless of course they are suggesting that you are a gangsta too.
I make no apology for the facetious, useless, and altogether incorrect nature of this post