NO MEANS NO !
Just as it says "No" is no, not maybe or later or keep asking or any number of things you might have wished was said instead of "No".
A person does not have to be rude to say no. Anyone can say no in a polite way. If you are the object of the 'no', be you a single male, single female, or couple, you need to learn to read others not interested clues.
When in doubt it is better to leave it alone. If you are not sure if he, she, or they, said 'No' leave it to them to make the next move. If the person or couple you approched is interested they will let you know.