I completely agree. This is clearly a missing feature in the UI macro palette in Asciidoctor. Would you mind filing an issue in GitHub?
I don't mind using the macro name "label", though we could also consider "lbl" or something else that's 3 chars or less.
lbl:[Name]
This can be used to identify any text in a user interface...though most often it will be for a form label.
-Dan