Commercially available stepping stone forms are generally made of plastic. Embossed in the plastic is the pattern for the surface of the stepping stone. It might be a plain, smooth surface for which you can tint the concrete to make plain, variously colored stones; or it could have a fancy pattern like a Mayan calendar or a flower. Some even have patterns that resemble the surface of natural stone.
Some concrete molds come in sets that have several sizes and shapes. These sizes and shapes fit together in a completed geometrical pattern that corresponds to an identical completed pattern. Similarly, some stepping stone mold sets have differing sizes and shapes that are not designed for an established, repeating pattern, but that can be creatively fitted by the home landscaping do-it-yourselfer.
Stepping stones can be assembled from simple parallelogram paver designs. These can be easily built using framing lumber, in much the same way bricks are molded. The difference is, the do-it-yourselfer is not restricted to standard sizes. He can graduate paver sizes to neck down or spread out or shift shapes. Individually sizes stepping stones can be molded for variously sized points in the yard or garden.
Some molds -- commercial and homemade -- are made with the stepping stone surface facing up. The form is only there to create the general shape of the form, leaving the surface available for the creative stepping stone maker to create his or her own designs. A popular design idea for face-up forms is the mosaic. Mosaics can be made with colored glass, bits of broken plates or pebbles.
The handy and creative form-maker can actually make some extra money producing stepping stones in his or her own molds. Anything that holds wet cement can be converted into a stepping stone form. The fabricator then adds tints to the cement or designs to the surface. An interesting press-in design on the exposed surface can make your stones unique. Some people also use hands, sand designs and leaves to make an interesting surface for the stepping stones.