Percy's first sign that retrieving the shield was a trap was the discovery of the word "eta" on the lifeboat, signaling the involvement of a figure associated with betrayal and rebellion against the Olympians. This moment triggers Percy's awareness of the potential dangers they face on their quest.
In Rick Riordan's "The Sea of Monsters," Percy's first sign that retrieving the shield was a trap occurred when he noticed the word "eta" carved into the side of the lifeboat. This discovery takes place when Percy, Annabeth, and Tyson are on their quest to retrieve the Golden Fleece and encounter the sorceress Circe on her island.
The word "eta" is the Greek letter E, and Percy recognizes it as a symbol associated with the Greek mythological figure Ethan Nakamura, a demigod who had turned against the Olympians. This revelation raises suspicions for Percy, indicating that the situation may be orchestrated by someone with ill intentions.
As they proceed, other warning signs emerge, such as the shield being attached to the boat with a cobweb, a detail that underscores the magical nature of the trap. Additionally, Cupids appearing and shooting arrows, creating a web above them, add to the ominous atmosphere, suggesting that love and desire might be manipulated for deceptive purposes.