Spoilers ahead for Star Wars: The Last Jedi!
Part of Kylo Ren's transformation to the Dark Side involved him killing his own father, Han Solo, in The Force Awakens — that was the idea, anyway. And while the infamous smuggler is certainly gone from the Star Wars movies, his presence is felt more than ever in The Last Jedi.
Leia, Rey, Chewie, and Luke are all reeling from his shocking and tragic death, and even Snoke realizes that the act of murder has split Kylo in two rather than solidify his love for the Dark Side. Having been an integral part in the destruction of both Death Stars and then Starkiller Base, Han is remembered by those who fight against galactic evil in a very special, yet obscure way.
Yes, Han Solo is in The Last Jedi, just not in the way you expect. In The Art of Star Wars: The Last Jedi, by Phil Szostak, it's revealed that the Resistance paints messages and intimidating faces on their Magna Bombs. Among the messages, which are translated from some alien language, are "Hi, Snoke" and "Han Says Hi" (with a little smiley face). It's good to know Han's wicked sense of humor didn't die with him.
This practice of writing on bombs actually happened during World War II, where Allied troops would write messages to Adolf Hitler on bombs before they were dropped on Nazi Germany. Fighter plane nose art (i.e. giving a bomber mean eyes and shark's teeth) was also popular at the time.
On the subject of bombs, the film's Visual Dictionary also answers the question how the Resistance drops bombs in space. Technically, they're not dropped, but magnetized toward a certain target, hence the name "Magna Bombs." "Bombs don't technically drop in microgravity, but are impelled from their racks by sequenced electromagnetic plates in the clip," writes the book. "The bombs are then drawn magnetically to their unfortunate targets."