One may be fooled by the acronym and thereby draw false conclusions and this may in the end just be an early version of "Kilroy was here" type of graffiti. Something like Dario Dante Tomassetti... ?

However typhus was a serious problem in the Mediterranean countries and there were significant outbreaks as late as the 1970s. Killing off disease-carrying lice and other bugs was therefore an early and very obvious use for DDT and it seems quite plausible that this was done in this particular village on May 26 somewhere in the 1950s... Kind of brutal marking though - maybe this building was abandoned already back then...