As Salaamu Alaykum, Is it correct that the cross on the first aid box is the sign associated with the Christians or is this a misconception? Also if one uses such a thing do they become a disbeliever, for example at work where they most likely wont be allowed to erase it?

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 is His slave and Messenger.

The sign of the cross of the Christians is what refers to a crucified man, so this sign is two intersecting lines at right angles to one another, and the top part of the vertical line is shorter than the bottom part of it, but now it is often drawn in equal lengths like the sign of the International Red Cross, which is found on ambulances. Such a sign must be removed and should be replaced by one of the slogans of Islam, like the crescent that the Red Crescent uses as its symbol instead of the Red Cross.

According to the most preponderant opinion of the scholars, it is not permissible for a Muslim to possess something which contains the cross before erasing it or changing it because it is confirmed that the Prophet would not see anything in his house which contains the sign of the cross except that he would erase it. [Al-Bukhari]

Ash-Shawkaani said: “The Hadeeth is evidence that it is not permissible to use/possess clothes or curtains or carpets or anything else which has images.”

The meaning of erasing includes covering the cross by sticking something on it which hides its features.

The Permanent Committee of Iftaa’ stated: “With regard to the mat on which there is a sign of the cross, it is disliked to pray on it except after erasing the image of the cross in a way that hides it by dying it or knitting over it or the like.”

Finally, it should be mentioned that a Muslim does not become a disbeliever just by using something that contains the sign of the cross like the first aid box, and if a Muslim is unable to change it, then Allaah does not charge a soul except according to what He has given it.

Allaah Knows best.