I noticed the Buttons section of the Designing for Playdate documentation says the following:
When instructing the player about your game’s UI, it’s helpful to enclose the A and B in circles... We provide glyphs for this in many of our fonts, mapped to the following characters:
Ⓐ Ⓑ
By the way, we have also font characters for other Playdate buttons:
⊙ ✛
These are not supported in Pulp fonts at the moment.