Apparently this was written by a member of the Armed Islamic Group of Algeria. Not that it has anything to do with Islam, of course.
On Saturday morning a parishioner discovered the graffiti on the wall of the Saint John the Baptist church in Bourgoin-Jallieu. These were done with a marker on two pillars, and on a notice on a panel at the back of the church. The messages were signed GIA, which may be a reference to the armed Islamic group. [Armed Islamic Group of Algeria].