Photos as art and education; I Read Symbols and I Read Signs, by Tana Hoban. New York: Greenwillow Books. 32 pp. $10. Ages 2-7.

Tana Hoban, prize-winning photographer, once again gives her followers an ''eye's worth.'' Her two new books are colorful presentations of vivid, point-blank photographs of traffic signs and signals seen along streets and highways.

From the image of the upstretched hand ordering us to ''stop,'' to the arrow saying ''go left,'' to the car on the squiggly black trail warning ''slippery when wet'' - these photo displays are both art books and straightforward educational tools for children. The books seem to say to the child, ''Let's take all those squares, triangles, and rectangles that we always see when we're driving, and just look at them, all by themselves.'' The result is an honest appreciation of signs for their color, shape, and content.

By studying both books, children are given the opportunity to become more observant of specifics of their environment, while gaining increased confidence in interpreting it. At the back of ''I Read Symbols'' is a log describing the symbols.

''I Read Signs'' literally speaks for itself. It's those commonplace directives like ''people working'' and ''pitch in.'' Again, the art resides in singling out these signs and bringing us face to face with their intrinsic, often surprising beauty.

Both books are good exercises in ''nominating'' familiar images. They earn their keep as effective learning tools - instructing the young reader in signs and symbols, while encouraging us to not let familiarity blind us to beauty.