Imagine a world where we were the ones claiming the cross is not a religious symbol. Perhaps there'd be a billboard claiming it for all of us. The christians would be furious.
And if they believed the claims made to justify crosses in classrooms or on public land were sincere, they would be even more outraged. One of their own! Disowning the cross. For shame! Jesus would be turning in his grave!
But we all, atheist and theist alike, know that this is just a nod and a wink. Of course *this* is a secular cross. It doesn't endorse any specific religion. It just symbolises death. The grim spectre of death that lurks over us all. (Now that I've engaged your fear of death can I offer you some religion?)
How long until a christian claims with a straight face that what they have erected is just a giant plus sign, meant to convey their appreciation for maths?