I am not familiar with what Tertullianus wrote about the cross....can you quote it ?
The cross was never popular until well after Constantinius banned crucifixion .
The fish was in wide spread used before the concept of an official body existed.
beyond its religious meaning, the crucifix symbolised the principles and values which formed the foundation of democracy and western civilisation, and that its presence in classrooms was justifiable on that account.
It referred on that point to its earlier case-law in which it had held8 that having regard to the preponderance of one religion throughout the history of a country the fact that the school curriculum gave it greater prominence than other religions could not in itself be viewed as a process of indoctrination. It observed that a crucifix on a wall was an essentially passive symbol whose influence on pupils was not comparable to that of didactic speech or participation in religious activities.
"The Court also considered that the effects of the greater visibility which the presence of the crucifix gave to Christianity in schools needed to be further placed in perspective by consideration of the following points: the presence of crucifixes was not associated with compulsory teaching about Christianity; according to the Government, Italy opened up the school environment to other religions (pupils were authorised to wear symbols or apparel having a religious connotation; non-majority religious practices were taken into account; optional religious education could be organised in schools for all recognised religious creeds; the end of Ramadan was often celebrated in schools, and so on). There was nothing to suggest that the authorities were intolerant of pupils who believed in other religions, were non-believers or who held non-religious philosophical convictions.