If you’re a big fan of Starbucks’s iced beverages, then you’ve likely noticed the raised dots along the bottom edge of your cup. They’re subtle, and they’re not just there for decoration.

But while Starbucks' unique mermaid logo has been with the company since it opened in 1971, its equally iconic cup sizes came a few years later. Starbucks didn't sell brewed coffee until the 1980s ...