Verb
(idiomatic) To ask for with no chance of success.
Used other than figuratively or idiomatically: see whistle, for.
Source: en.wiktionary.orgI'm in the Lord's hands,' he said humbly. 'I'm but a penny whistle for His breath to blow on.' This he said with such solemnity that the meaning of a fanatic was suddenly revealed to me. One or two distorted notions, a wild imagination, and fierce passions, and there you have the ingredients ready. John Buchan
When a dog runs at you, whistle for him. Henry David Thoreau
Moyo was happy at the final whistle for a powerful comeback, attributing the late surge to his half-time pep talk which lifted the the spirits of his players. Source: Internet
Participants each received a new Fox40 whistle for taking part in the session. Source: Internet
Pereira was sent off after the final whistle for Northampton, for dissent. Source: Internet