Kissing the Black Stone during tawaaf is Sunnah mu’akkadah (a confirmed Sunnah), it is one of the Sunnahs of tawaaf if it is possible to do that without crowding or disturbing anyone by your actions, following the example of the Messenger of Allaah (peace and blessings of Allaah be upon him) in that. If it can only be done by crowding and disturbing others, then it should not be done; in that case it is sufficient to point to it with one's hand, especially for women, because the woman is ‘awrah and because crowding is not prescribed for men, so that applies even more so to women. If it is easy for a woman to kiss the Black Stone without crowding, it is not permissible for her to uncover her face when doing so, because there are men who are not her mahrams in that place.