Before you start submitting your short film to competitions, distributors, websites and festivals, it is important to know what your rights are to all the materials, all the content in your film.
Basically, whatever is in your short film – from brand names, logos, products (no matter how low-key they may be), must always be cleared before you show your film to the public. If your story evolves around two characters enjoying a meal inside a famous pizza chain, you need to get clearance from them before using their name, brand or store in your film. Or, if you are shooting a character in gear that displays a logo loud and clear, you also need clearances.
Similarly, if you are using stock footage from anywhere in your short film – be it news footage or other clips – you need clearance for these. Same for photographic images, graphics or illustrations, fonts or texts or designs – even a famous painting, if you are including it in your story, you need to make sure it is OK to do so.
If you are hesitant about some of your content, always seek the advice of a lawyer who can help you – many lawyers do pro-bono work for emerging artists and creative people, so ask around to find someone.