Cities around the world have festivals that they advertise on street pole banners. These same festivals usually have parades. And it is up to local law enforcement to secure the people involved. This is because they want people to enjoy these festivals.
However, given that these are immensely public events and people flock to specific areas, terrorists could easily plant a bomb and cause genocide. This is what local law enforcement tries to prevent. After all, they also wouldn’t want the city’s security reputation to be tarnished. Otherwise, tourists and investors wouldn’t want to visit that city.
The local security force first needs access to the plans for the festivities. To do this, they coordinate with city officials. They then survey the area where the festivities are going to take place in. They set up blank flags where they have to set up observation teams. They will also have to make sure that these observation areas remain civilian-free. At different points along the path of the parade, different crisis management teams are stationed alongside visible police outposts. This way, any emergency can be dealt with efficiently.
The reason why city officials want these events to be protected and observed is because they want to preserve their relationship with the sponsors. This is because they know that if anything happens, future sponsors would be reluctant to fund such an event. After all, they are spending a lot of money for something. And they have their names etched on that event. If something happens, their name goes down with it. To protect them, the city officials have to protect the events where their corporate flags are displayed.