Near me, it is fireworks.
Sometime after Memorial Day weekend, the seasonal shops open up for selling fireworks.
It's technically illegal to set off fireworks on days that aren't a holiday (or adjacent to a holiday on the calendar). However, the region has had fireworks in the air most weekends since the end of May.
More recently, it's been many weeknights, too.
This is a significant change, but probably affected when the State normalized the sale of fireworks. Previously, anyone who wanted to celebrate the Fourth of July had to go out of State (or to an Indian Reservation) to purchase fireworks. This had become common enough on the 4th of July that eventually the State legislators figured out a way to make sale of fireworks legal in the State.
Once it became legal to perform such business locally, the locals began purchasing fireworks (and setting them off) on a regular basis in the Summer.