It's mentioned in the The Hawaiian Archipelago (1831–1904). Essentially three cheers followed by a loud growl from the crowd (the "tiger").
On the king's appearance, the cheering was tremendous,—regular British
cheering, well led, succeeded by that which is not British, “three
cheers and a tiger ,” but it was “Hi, hi, hi, hullah!”
There's another description mentioned here from an article called The Artilleryman's Glossary, apparently dating from the 1870s.
THREE CHEERS AND A TIGER - when "Three cheers and a tiger" was called
for, there is division as to what that represented. There is no
apparent dispute that the first portion - the "Three cheers" -
represented three "Hurrahs!". The "tiger" portion of that is argued as
either a growl from the crowd, slowly rising in volume and pitch until
it became a roar of approbation; while others contend that it the
addition of the chant "Hi! Hi! Hi! Hi!" at the end of the third
"Hurrah!", the series of "Hi!"'s also rising in both volume and pitch.
Evidently the Princeton University cheer used to include a "tiger".
Multiple cheers evolved throughout the latter half of the 19th century, including "The Tiger," "The Rocket," "The Princeton Cheer" and "The Tiger and Rocket," which morphed and intertwined over time, including:
Rah! Rah! Rah! S-s-s-t! Boom! A-h-h-h!
Hurrah! Hurrah! Hurrah! Tiger! S-s-s-t! Boom! A-h-h-h!
Hooray, hooray, hooray! Tiger siss-boom-ah, Princeton!
And we also have an example within the story itself
EVERYBODY. (Except Stephenson, who bows with hand on heart) Hip—hip—hip: hurrah, hurrah, hurrah!
GR. Der Tiger—ah-h-h!