"We try to always keep the public informed any time we know of an event that might generate interest or concern," said Patti Mullis with the city.
There may be concern when in a movie theater parking lot off a busy stretch of town, residents might see people in SWAT gear, simulated weapons and a general chaotic scene.
The city didn't feel it needed to but rather wanted to alert the public so no one thought what they may witness was a real mass shooting or other emergency situation.
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"We've had other film production crews that involve similar materials and we're just aware that if someone were to drive by and see someone with what looked like a weapon or SWAT gear, they might think something is going on," Mullins said.
It is unclear what they are filming or what it may be used for, but the city of Frederick wants to let its residents know it's Hollywood, not Frederick.