The Ancient Man Snake couldn't mark Ge Castle; the star was hiding within the God Star, making it impossible to distinguish it from the Star Flame of the God Star, just like you cannot distinguish a drop of water from the ocean unless that drop is ink.
So the Ancient Man Snake announced a reward because it knew there existed a power in the Void capable of turning ordinary water into ink — it had seen it firsthand.
Shamara's inspiration shouldn't be overlooked, thus the reward was announced. The Divine Star Shadow received it and contacted the silver coin while Olette received it and found Lightning and Luther; however, they were all despicable middlemen offering very low bounties.
Olette even wanted to use White Crystal as a reward, which led Ange to discover its ability to detect White Crystal — these crystals were actually excavated from the Tree of Ten Thousand Realms, much to Anthony's delight, for items that can be excavated from the tree are inexhaustible.
