A sun (typically gold sun on green field if memory serves) is a common Rohirric motif -
When Aragorn, Legolas and Gimli arrive at Edoras -
The dark gates were swung open. The travellers entered, walking in file behind their guide. They found a broad path, paved with hewn stones, now winding upward, now climbing in short flights of well-laid steps. Many houses built of wood and many dark doors they passed. Beside the way in a stone channel a stream of clear water flowed, sparkling and chattering. At length they came to the crown of the hill. There stood a high platform above a green terrace, at the foot of which a bright spring gushed from a stone carved in the likeness of a horse's head; beneath was a wide basin from which the water. spilled and fed the falling stream. Up the green terrace went a stair of stone, high and broad, and on either side of the topmost step were stone-hewn sea, There sat other guards, with drawn swords laid upon their knees. Their golden hair was braided on their shoulders the sun was blazoned upon their green shields, their long corslets were burnished bright, and when they rose taller they seemed than mortal men.
I think there's other references as well, but can't find them at the moment. And it's all over the WETA interpretations.
I suspect inspired by the sun-motif of the Indo European horsemen, but I don't know how much that's out there now was known when the Professor was writing. It makes sense I suppose - if you spend all your days on a great grassy sea with few trees to speak of overhead, how can you not be constantly aware of the sun?
(kinda reminds me of Lakota, etc. sun motifs as well, now that I think on it)
Persona: Aerlinneth, DÃºnedain of Amon Lendel c. TA 3010.