A whistle can signify a spiritual summons and shares the significance of a wind instrument. A whistle may be heard and recognized in dreams about games. As a means of imposing control and training, it may be relevant as to how it is blown. For instance, if it is blown harshly, we may be being made aware that we have transgressed a known code of conduct. A whistle being blown in a dream can mark the end of a particular phase of time. It can also sound as a warning to alert us to a particular event. To clarify your interpretation consult the entries for Games and Musical Instruments.