Whimsical all the way: Sometimes art is just that; a way of saying something funny or whimsical in such a way that it reaches the largest section of the population as possible. It combines a cute leaf on the street or some really simple part of everyday life and make it into art.
Serendipitous art: Serendipitous art is the kind where an element is just perfect for rendering the art. Like bricks on a wall forming the books that you want to depict or stairs as piano keys. This way the art is easy enough to come up with given some of the elements are already present.
Macabre and gory: Sometimes street art can show gory stuff in the form of art. This could be because the artist is into such sort of art or because he or she is using it to pass on a deeper message that may become clear once the viewer looks at it.
Part of fun and entertainment: Art in a way is supposed to engage and entertain you and this is sometimes the only trait that street art is supposed to have. Imagine having the picture of a stooping person looking down at you from a building using a magnifying glass? It can be serious fun!
As we said, art without boundaries is the way to go and street art definitely follows the credo. The artist has immense freedom of expressing what he or she wants on a really large scale. The audience is also larger but the only thing that street artists have to remember that they have to make that extra effort to make it commercial. Actually, there have been many instances where street artists have made it big commercially.