Large.  14" x 24".  The white enamel is in strong relief.

This is from District 16 in the centre of Paris - this street is roughly equidistant from Roland Garros Stadium, Eiffel Tower and Arc de Triomphe.

Gustave Zédé was a marine engineer who designed France's first electricity propelled submarine in 1877, built in 1880.  He went on to design and build others.  This street was renamed in his honour in 1912.  This sign dates from then and is an early version of Parisian green rimmed signs - see how much of the green has been lost on all of the original signs shown.  The loss of detail such as white piping is also common among the earliest examples of vitreous enamel fused onto sheet steel.

The fourth image is the Wikipedia reference photograph of the street sign in place.  Identical but not the same one.  The fifth is that sign showing more of the street.  The sixth is of the sign at the other end of the street and the seventh of a more recent example.