Filmmakers should supply Film Festivals with their film’s hashtag at the time of application to the festival and then stick with it. Which of course means filmmakers should select a hashtag early and not deviate from that hashtag.
Which brings up the question of “what makes for a good hashtag?”. Short. Distinct. Recognizable. Easy to remember.
The hashtag is how people can communicate about the film across all social media. It is a search device. Ideally then the film festival can use your hashtag whenever the film is mentioned.