Clothes irons that were heated in front of fires began to be used in europe from the 17th century (the use of heat was employed much earlier in china). Previously wrinkles had to be removed without the benefit of heat and were usually placed upon a flat board and smoothed with a wooden roller - good times they were known as sad irons, sad' being an old english word for solid'; though the term flat iron' became more common.
This french antique sadiron is one of the nicest i've seen, with clear, crisp text and ornate decoration. Note the sharp detailing of the (laurel) wreath and bow, the tiny pair of scissors, etc. 5 denotes the size of the iron.
This is almost certainly incorrect. Rather they must be guild markings this one is "jardinier", and i have a "gendarme" one as well. Additionally, i read that the no. 5 indicates the iron weighs five kilos - this is simply not possible, as while it is heavy, it is not remotely 5kg. It likely simply refers to the size of the flatiron, as in descending order the dimensions are smaller as well.This item is made of cast iron.