Security forces and a bomb squad were called in after two men alerted them to the disturbing display in the bathroom of the 1930's cinema last weekend, local media reported.
The messages displayed around the two cartridges included references to the recent Charlie Hebdo cartoon which likened victims of the central Italian earthquake to lasagne, along with the phrase 'Everyone has their own reasons'.
These notes were accompanied by signature that allowed police to track down their creator - a 40-year-old artist and father of five from Cagliari in Sardinia, La Nuova Sardegna reported.
As for his own reasons, he will have to explain them to police, who have charged the artist with wasting police time and possession of firearm parts.
After a thorough search of the area by Digos, the Italian law enforcement agency charged with anti-terror operations, it was declared safe.