LTS is "Laugh To Self" - A variant for LOL (Laughing Out Loud)
A portrayal of good humor - before reaching the LOL stage.
People often type LOL when they aren't really LOL. 11 year old Kristen Tobey from Fort Wayne, IN noticed this and started encouraging friends to type LTS for gathering humor, which caught on. This opens the door for more shortcut terms in degrees of chuckle.