If I was this chap, I would simply transfer the cross symbol from decorating the vehicle to decorating myself, then there would be no breech of policy.  Instead he's trying to make the case appear as if it's a case of discrimination, where Christians are being treated differently from other religions, which isn't true.

Martin, its a palm cross, which is difficult to decorate oneself with. As such, this is a a form of discrimination - not so much of Christians, per se, but of quite what one is allowed display of one's faith.  Ironically, Christianity has possibly the lowest number of compulsory symbols - none (after all, none of us are required, as part of our faith or denominational belief, to display any symbols).  I wonder why crosses seem to offend people so much?

I think the other issue is that the company would appear to be being inconsistent in the application of their own policy.  If they had applied it consistently, why hadn't this guy been told to remove his symbol long before this complaint was made?  Surely the van is checked on a regular basis.  As such, it would smack of hypocrisy on their part - and I can see why the guy is querying the decision.