Green’s Dictionary of Slang

eighty-eights n.

[orig. used by telegraph operators]

(US) love and kisses.

[US]Weseen Dict. Amer. Sl. 166: Love and kisses, in the lingo of telegraph operators....88’s.
[US]L. Dills CB Slanguage.
P. Wood Salt Book 175: 73’s [&] 88’s [on a business card, without further explanation].