I have heard the announcers at various games ask the fans for cooperation and cite the CIF motto of sportsmanship. At tournament, CIF officials have gone into the stands to ask fans to tone down their comments. I can't recall ever seeing an umpire speak with a fan, although I do remember an umpire speaking with a coach and asking him to talk to the fans.
We had a Dad who really had a hard time, especially when his son was pitching. We, the others parents would talk him through games; eventually he decided to sit out in left field - it was just easier for him.
Funny though. A school in our league is well known for their parents, ahem, unsportmanlike comments. Our pitcher (who has a hearing deficit) always talked about the GRAND parents who would start talking in trash before the game even started. We knew it had to be loud because he had a very hard time hearing his coaches instructions from the bench but could hear grand pa sitting in his lawn chair behind home plate.
Repeated comments from our coach to their coach, then from our AD to their AD, and eventually principal to principal didn't help contain these folks.
Last year, on our home field, our AD and principal were in the stands. When Grandpa started with his trash talking, they went down and very politely escorted him from the field. The other parents all made notes -- I'll be interested to see if the behavior improves this year -- at least on our home field.
Now that our pitcher is in college we've had a bit of culture shock. It isn't that the parents are out of line, but we've spent 4 years without hearing "colorful" language or strongly worded suggestions to the umpire about strike zones.
Say Hey!