Open Signature List…

Opens the Signature list. The Signature list contains key signatures and time signatures.

Logic Pro time and key signature overview — Apple Support

When you create a project, the key signature defaults to C major, unless you choose a different key signature. The initial key signature affects the playback of Apple Loops in the project. Key signature changes affect the display of MIDI notes in the Score Editor, but do not have an effect on MIDI playback.

Logic Pro time and key signature overview — Apple Support

The Signature List displays time and key signatures in a numerical list, and also displays global score symbols such as repeat signs, double bar lines, and so on.