Look up tallyho in Wiktionary, the free dictionary.
Tally-ho is the traditional cry made by the huntsman to tell others the quarry has been sighted. It may also be used with directions, including "away" and "back".
First used in fox-hunting, it was adapted in the 19th century to describe some horse-drawn vehicles and in the 20th century to advise of enemy aircraft and space junk.