Attentive tourists may notice that there is some strange dark spot that looks like either a stone defect or a fungus on the tower clock of the Horse Guards Clock in London. It is located right at the 2 o’clock mark.

The black mark on the clock face is not dirt or mold. This dark spot marks the time of the execution of King Charles I, near this place on January 30, 1649, at 2 p.m.