A time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day.

One sort of public time signal is, of course, a striking clock. These clocks, however, are only as good as the clockwork that activates them; they have improved substantially since the first surviving clocks from the 14th century. For many members of the general public, a public clock such as Big Ben was the only time standard they needed.

When more accurate public time signals were desired for use in navigation, a number of traditional audible or visible time signals were established for the purpose of allowing navigators to check their marine chronometers. These public time signals were formerly established in many seaport cities.