Firstly: 

In the answers to questions no. 135279 and 121170 we explained the ruling on making crosses and putting them on clothing or walls, and the difference between the cross which it is forbidden to make or hang up, and that which resembles it but is not regarded as the kind of cross that it is prescribed to remove and is prohibited to buy, sell or hang up. 

Secondly: 

With regard to these images in the form of a cross that are hung up in classrooms and lecture halls, we should examine the matter first of all, and determine for what purpose they were made. Are they made to look like the cross which is a symbol of Christianity, or are they just patterns and adornments on the wall, or design elements that look like crosses? 

If they are the first type, then what is prescribed is to dismantle and remove them, because they are symbols of the Christian religion, and if the Muslim is able to remove them himself, then what is prescribed is to remove them, and he should forbid putting them up, because of the report narrated by al-Bukhaari (5952) from ‘Aa’ishah (may Allah be pleased with her), that the Prophet (blessings and peace of Allah be upon him) did not leave anything in his house on which there were crosses but he removed them. 

Al-Haafiz (may Allah have mercy on him) said: 

Because the cross is something that is worshipped besides Allah. End quote. 

If it is of the second type, which is if it is a kind of pattern and adornment, or design elements that is not intended to look like crosses per se; rather it is something that happened coincidentally, then it is not required to remove it. But it is a good idea to change it so as to avoid any resemblance to crosses. 

Thirdly: 

If it is of the first type which is forbidden, then what must be done is to change it by taking action and removing it and forbidding it, if it is possible to do so. If it is not possible to do so, or if removing will lead to greater harm or trouble, then what one must do is denounce it, forbid it and encourage its removal verbally. If it is not possible to do any of that, then one must disapprove of it in one’s heart. 

Muslim (49) narrated that Abu Sa‘eed al-Khudri (may Allah be pleased with him) said: I heard the Messenger of Allah (blessings and peace of Allah be upon him) say: “Whoever among you sees an evil action, let him change it with his hand (by taking action); if he cannot, then with his tongue (by speaking out); and if he cannot, then with his heart (by disapproving of it and feeling it is wrong), and that is the weakest of faith.” 

In the answer to question no. 12812, we explained that if denouncing an evil will lead to a greater evil, then it is not permissible to denounce the one who does it. 

In the answer to question no. 96662, we explained that one of the conditions of enjoining what is right and forbidding what is wrong is that the Muslim should be able to do that without bringing harm upon himself. If it will bring harm upon him, then it is not obligatory for him to do that, because everything that is obligatory is dependent upon being able to do it. 

If the administration of the university insists on not changing or removing these crosses, then the Muslim must continue to disapprove of it in his heart, and if he is able to change his place of study without that being detrimental to his interests, then he should do that and his reward will be with Allah. 

What is prescribed is for the Muslim, in the first place, to choose a suitable environment in which to live and study, and if he is faced with something contrary to that and is not able to change it, he should denounce it and disapprove of it according to what he is able to do, and there will be no blame on him. 

For more information, please see the answers to questions no. 112188 and 127946 

And Allah knows best.