What is the ruling on displaying a sign with which Allah has blessed His servant (knowing that one is quickly affected by the evil eye)?

Speaking of Allah's blessings is part of perfecting gratitude for them. Allah commanded His Prophet with this, saying: "But as for the favor of your Lord, report [it]." (Quran 93:11), meaning, publicize what Allah has bestowed upon you as a sign of gratitude and praise. This command is for recommendation, not obligation, as it is impossible to enumerate blessings. If reporting them were obligatory, it would be an imposition of what is beyond one's capability. Thus, displaying blessings as a form of gratitude is recommended.