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.
“Church Vandalised in France: ‘Death to France, Long Live Islam, Long Live Bin Laden,'” by Cheradenine Zakalwe for Islam Versus Europe, June 15 (thanks to The Religion of Peace):
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].
Source: LeDauphine.fr