I've traveled widely throughout Chicagoland for years. The New Trier School District is the only place where I see a concentration of signs in front of homes announcing milestones passed by the children who live there.
Although high school graduation is an achievement, it's one that's routinely expected on the North Shore, so a bit surprising that it's so widely celebrated in signage.
If you're visiting Wilmette, Kenilworth, Winnetka, Northfield or Glencoe in the near future, you're likely to see many signs like the ones above. New Trier bumper stickers are a year-round staple.