There are a number of haraam things involved in wearing the masbahah around one’s neck:
1-Imitating the innovators and Sufis; it is not permissible to imitate the people of innovation (bid’ah).
2-It is a kind of showing off, so that it will be said of the person, he is one of the people of dhikr; or it is like showing off, or it opens the door to impugning his honour as it may be said that he is showing off.
3-It may lead to ignorant people imitating him because they think that it is something good, as they may think that there is some reward for wearing the masbahah around one’s neck.
4-It may lead to people believing that this is a form of protection that wards off evil.
5-He may seek blessing from it and believe that it brings good.
6-If there is some adornment on the masbahah, then it is an imitation of women, because they are the ones who wear necklaces around their necks.
7-It may be a means of fame, because people will point at him and his strange appearance.
And Allaah knows best.