Almost anything can be considered as public art.
In years past, monuments, memorials and civic statuary were commissioned and put on display in a prominent location such as a park, courtyard or town square. Public art in those times was large and constructed of durable materials such as bronze, stone and cementious materials.
In recent times public art has come to include displays such as: street furniture and lighting, and now graffiti, dance, and street theater come under this heading.
The best place to observe public art in my home state of Hawaii is in downtown Honolulu. Here industrial areas are littered with graffiti, plazas in the urban core are punctuated with large sculptures and the pedestrian promenades have sculptural lighting and benches. Heading to the north shore and getting away from the urban intensity of Honolulu the steel and concrete gives way to narrower roads and open agricultural lands. Public art in these locations is relegated to graffiti and murals painted on the sides of buildings.
In the outer islands of Maui, Hawaii Island and Kauai there is little public art. On Maui, the towns of Wailuku and Kahului have outlawed graffiti, but murals in prominent locations are allowed, and the following examples display much of the Hawaiian culture.