I spoke because Joan is trying to get the stone then meets jack and he goes with her to get it and the money she owes him, the tile fits because they kind of fall in love along the way so it's romance and a stone 8)
The lead female character is a "romance novelist", meaning, she writes romance books. Also, later in the movie the Danny DeVito character makes a reference towards this movie title by saying to Joan Wilder, "You're not going to romance this stone out of here..." or something to this fact.
By the end of the movie, she writes a romance book about this adventure she had.
_ Every person that served can be called a veteran, but not every veteran can be called a Marine.
However.....it's called that because it's a play on words.
There's romance, there's a stone, sure. But it's also an expression meaning to make a crude gem elegant by refining it. (Which, one could argue is an analogy of Jack and Joan's relationship)