Luto nacional oficial.

Lockdown day 81.
The flags outside the municipal buildings and on ships are being flown at half mast, and additionally show a black ribbon. Many householders too see fit to display this flag on their balconies (extra).
The reason is because Spain is in the midst of paying a 10-day tribute to the 27,000+ killed by COVID-19. This is the longest period of national mourning in the country's democratic history, will end at 00:00 on June 6, and will be marked by an address by King Felipe VI. 
Prime Minister Pedro Sanchez said:
"Those who died in this epidemic deserve our lasting memory. They deserve even greater homage: our coexistence and societal harmony. Together we must live in the same country they built. Spain owes it to them."