There were already signs scratched by humans on walls in the Paleolithic Age, but they have only been known as 'graffiti' since the archeological excavations in the Roman city of Pompeii began in 1856. Graffiti are often spontaneous, illegally installed, author-referenced messages; unvarnished truths aimed at the general public or simple signs and drawings. As from the end of the 1960s they were no longer merely scratched or written in charcoal or chalk, but also executed with a marker or a spray can. This modern form of graffiti is also referred to as style writing or hip-hop graffiti.

Increasingly, as early examples from around 1967 in Philadelphia and New York show, the writing of one's own name became more important than the message itself. Now, the priority was on the quality, style or quantity of the written signs. With a spray can it was possible to create big, colorful name pictures, genuine 'masterpieces'. At its highest quality, the writing of an alias – pseudonym – with a marker, so-called tagging, generally reviled by the public at large, can attain the level of calligraphy and gestural, abstract painting.

In street art it is images that dominate rather than text. Like graffiti, street art is created illegally. Unlike graffiti, however, it aims to broadcast messages. Mere names, to the fore in graffiti, do not have a role to play here. Quite deliberately, street art is to be found in places that fit in with the message or the form of presentation.

While graffiti, as a rule, is restricted to the use of markers and spray cans, street art comprises a fair number of techniques. The best known of these is based on the use of stencils – (pochoirs). Apart from that there are murals, paste-ups, fly posters and cut-outs, small-scale stickers, and mosaics and sculptural works.