Tactile walking surface indicators are intended to be detectable underfoot when walking or by a long white cane. They are used to alert people with low or no vision of potential hazards, such as moving vehicular traffic.

The indicators must also provide a high tonal contrast with the surround surface. The indicators that are installed in the City of Toronto are made of cast iron. Initially, cast iron will develop a rusty red colour which may stain the sidewalk in the first year following installation. The stain will eventually disappear and the cast iron will develop a natural patina, which provides an even greater tonal contrast with the sidewalk.