That is because the Day of the Cross (Día de la Santa Cruz) and the Day of the Construction Worker (Día del Albañil) are both on the same day in early May. They are connected because in the 16th Century, while excavating old Jerusalem, workers found three crosses. When they touched the largest of the three, they were healed of any sickness that they had. The cross was believed to be miraculous. The story goes on to say that a funeral passed by this excavation site and when the dead man, a construction worker, was made to touch the cross, he was resurrected.
And that is why we see crosses adorning construction sites across Latin America.
