All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.
Undoubtedly, this is a great evildoing and disrespectful to the Mosque of the Prophet, sallallaahu ‘alayhi wa sallam. May Allaah reward you best for your concern and worry when seeing the prohibitions of Allaah being violated, and may Allaah add this to the record of your good deeds. It is obligatory on everyone who knows about this evil to forbid it as much as he can.
The Prophet, sallallaahu ‘alayhi wa sallam, ordered the one who sees an evil to change it physically with his hand if he was able to do so. If he could not, he should change it by his tongue (by advising and/or condemning), and finally by (detesting it with) his heart, and he, sallallaahu ‘alayhi wa sallam, informed that this is the weakest level of faith. [Muslim]
Allaah Knows best.