Hi,

Thanks for comment!

Short answer - unfortunately, I don't know, I was walking there by foot and saw the sign when standing on the square and looking north on the left from bar Saitta. There were also signs indicating it is/was one-way only and there was a pedestrian crossing road-marked. Maybe as usual in Italy, no one cares about signs and in reality people still drive?

Just to make sure, here is this pedestrian sign on Google panorama, feel free to double-check https://maps.app.goo.gl/smVrPHdLKzJJn4uA7?g_st=ac

Long answer - the big part (if not whole) of Corso Umberto Primo is ZTL so it's not like many people drive there anyway. Plaza Nicola Spedalieri square itself had some parking markings, so one could drive thru it probably (just thru the whole square)
I would also suggest it might have been some temporary change due to Pistachio festival this weekend, but the pedestrian-only sign looked quite old.