Peace be upon you, Dr. Salah,

Is it permissible for a woman or a man to wear an engagement ring or a wedding ring? May Allah reward you well.

All praise is due to Allah and may peace and blessing be upon the Messenger of Allah, his family, companions and true followers. To proceed:

May Allah increase you in being careful and eager to learn what is permissible, and to follow it; and to learn what is prohibited, and to avoid it. May Allah grant you the best of rewards.

Know (may Allah have mercy on us and you) that, if wearing a wedding ring is accompanied by prohibited superstitions such as pessimistic expectations, for instance, if it isn't worn, imitation of non-Muslims, or (for men) if the ring is made of gold, wearing it would then be prohibited and its prohibition is a matter of agreement, not for the act of wearing it in and of itself, but for the other reasons mentioned.

As for a situation free of anything mentioned above, the rule is that it is permissible, though we advise you to suffice in that with a ring of silver for men and gold for women if there is a need for it or if it would be beneficial somehow, though I would like to call your attention to the fact that it is not permissible for a man to [physically] place anything of the sort on his fiancee because she is [still] "foreign" (non-mahram) to him.

The Prophet (may Allah bless him and grant him peace) said, "For one of you to be pierced in the head with an iron needle would be better for him than to touch a woman who is not lawful for him." [Transmitted by Imam al-Tabarani in his Al-Mu`jam al-Kabir and authenticated by Shaikh al-Albani, may Allah Almighty have mercy on them] It is certainly clear that your fiancee is still a "foreign" woman [she is not lawful for you]. All help is from Allah and He Alone is the Guider to the Straight Path.