semaphore

The Running Manを読んでいます。今日取り上げるのは難しそうな単語です。
The gun was knocked into the brush and Richards was on his back. The dog was on top of him, a big German shepherd with a generous streak of mongrel, lapping his face and droodling on his shirt. His tail flagged back and forth in vigorous semaphores of joy.
"semaphores of joy" は犬が喜んで尻尾を振っていることを示しているはずなので、表現の意味かしらと思いますが、とにかく辞書で確認します。
・Oxford English Dictionary: A system of sending messages by holding the arms or two flags or poles in certain positions according to an alphabetic code.; Use of semaphore flags was limited to within range of telescopes in earlier days and binoculars today.
・Collins Dictionary: a system of signalling by holding a flag in each hand and moving the arms to designated positions to denote each letter of the alphabet: Amy finished her whisky with a shiver, and held up her glass to semaphore a request to fill it again.
なるほど、元は手旗信号のことですか。