Hmmm. I did a little deeper digging. I'm working on a newer laptop. I thought I had Myriad installed, but I did not. As soon as I installed the Myriad family into FontBook app, the diamond went away. So the template was calling for a font that the OS didn't have installed, and therefore showed a diamond shape after the typeface name. Different in InDesign, the font name shows up with square brackets surrounding the [fontname].
Since the template did not already have type objects within it, opening the template did not trigger the Missing Fonts dialog box. But it did show the diamond next to the default character style fontname.