What is the ruling on a sister kissing her brothers in public places?

Kissing mahram relatives is permissible on the head, nose, or cheek, except for the mouth for anyone other than one's spouse. However, it is permissible on the mouth if the person is returning from a journey or similar circumstance, provided there is no fear of fitna (temptation/strife). As for kissing in public places, it is not recommended and is disliked because it compromises modesty and decorum, and it might be misunderstood, unless there are clear indications of the mahram relationship and both individuals exhibit signs of modesty and religiosity.