As the title indicates, these are details from various works of graffiti. Further, they are so relatively small in scale that you've got little sense of the larger work. There's no way you can tell that the last detail, that black square on a white background, if from a Jerkface image of Sylvester the Cat. Nor is it in the least bit obvious that the center target is from Sonet piece in the Bergen Arches (now two or three layers down. Still, if you look closely, and not all that closely, there are things to notice, the different surfaces for example. Of course the colors. And isn't it obvious that the second image shows some paint that has been splashed on rather than being sprayed from a can? And the first one centers of a silver square (with some white overlay at the top). Silver has a special place in the graffiti ecology, with a whole class of images known as "silvers" because their predominant paint (generally with black outline). And the fourth one, notice the pealed paint? How many layers are on that surface?