When the action takes place all at once, for example, I saw a woman, He came to dinner, the picto for Once () may be added. The explanation of this picto () can be seen in the section 30. Once, Twice, etc.
We put the sign only when we want to stress that the action was not continuous.
Sometimes it is interesting to indicate that the action was happening in a continuous way, that it was not instant. In this case we can make the dot somehow longer () so as to show a certain continuity of action.