In traditional heraldry, the Sun in Splendour is a "charge" or identifying symbol of a humanized sun, represented by a round disc with the features of a human face surrounded by twelve or sixteen rays, alternating straight and wavy (representing, respectively, the sun's light and heat).
"Brazen" is not a formal Heraldic term, but it has been used to poetically describe the sun since at least the 16th century. The word itself derives from the word for 'brass," and is something of a mystery word, with no known cognates beyond English.
Brass is an alloy metal with unique and highly useful qualities. It is shiny, more durable than gold, and more widely available. Brass can either be valued for its inherent properties or sneered at for mimicking the qualities of gold without actually being gold. So "brazen" or "brass-like," is a context word, and can be used to compliment or to insult.
The modern definition of brazen is along the lines of "having a quality of strength sufficient to ride out or through an embarrassing or difficult situation by behaving with apparent confidence--and lack of shame."
It is often used to describe people are very bold and seem not care what other people think about them or their behaviour.
🌒 Waxing Sickle,: In the Northern Hemisphere, we see the moon's waxing crescent phase as sickle of light on the right.
🌘 Waning Sickle: In the Northern Hemisphere, we see the moon's waning crescent phase as a sickle of light on the left.
From the Southern Hemisphere, these directions are reversed.
The Sicklemoon, then, is a symbol of change--and it is impossible, in a moon image shorn of context, to know which way that change is going.