Guillaume Apollinaire was a French poet. In a poem called calligram, the letters' arrangement has a meaning. Here is an extract of the collection of poems Calligrammes: 

This calligram is carved on Apollinaire's grave. The poet is buried in Père-Lachaise Cemetery in Paris. 

The text in French is: Mon Cœur pareil à une flamme renversée 
The translation in English could be: My Heart like an inverted flame