the Fatwa Department Research Committee - chaired by Sheikh `Abd al-Wahhâb al-Turayrî
If the necklace is made of gold or is in any way feminine, then it is unlawful for a man to wear it. Men are not allowed to copy women in their dress and customs. It is unlawful for a man to wear rings or a necklace, even if it is not made of gold, if such jewelry is construed by the culture in which he lives to be a mode of dress for women worn especially by women. It is unlawful to emulate women.
In an authentic hadîth, the Prophet (peace be upon him) said: “Allah cursed men who emulate women and women who emulate men.”
If the necklace is particularly masculine, we have the following ruling on it by Sheikh Sâmî al-Mâjid:
All praise is due to Allah.
It is alright for a man to wear such necklace as you describe in your question provided that he does not believe that it brings any benefit to him or protects him against any harm. The Prophet (peace be upon him) forbade Muslims from wearing amulets. He said that amulets were forms of polytheism. [Musnad Ahmad and Sunan Abî Dâwûd].
For this reason, the Prophet (peace be upon him), during a journey dispatched a person to cut all necklaces from the necks of camels. [Sahîh al-Bukharî and Sahîh Muslim]
And Allah knows best.
Source: Islam Today