What is the ruling on placing a temporary mark or crystal for adornment between the eyebrows, which is common among women in India?

The fundamental principle is that it is permissible for a woman to adorn herself with what she wears, unless there is a prohibitive impediment. If the brand does not impede the validity of ritual purity (taharah) and does not involve imitation of disbelieving women in what is exclusive to them, then wearing it is permissible. However, if it involves imitation of disbelieving women in what is exclusive to them, then wearing it is not permissible, due to the Prophet's (peace and blessings be upon him) statement regarding saffron-dyed clothes: "These are among the garments of the disbelievers, so do not wear them." And due to his statement: "Whoever imitates a people is one of them."