Well, UI Design is independent; the business owners can suggest ways to keeping UI clean and usable, but it's the job of the software developers to ensure a user can understand WHICH button to press. One characteristic that can set apart a gamepad button from a keyboard key is encircling any...
Simplicity is key IMO, if you want the greatest audience, you need to use universal language; this isolates greek letters and sequence values as well as symbols.
α, β, χ, γ or
1,2,3,4 / I,II,III,IV or
PSX style square, circle, etc...