how do i know if it is a redhat kernel distribution?

Is there any macro or any other means by which i can find out that the
kernel in my host is from Redhat?

From 2.6.12, sk_alloc signature changed from
struct sock *sk_alloc(int family, gfp_t priority, int zero_it,
kmem_cache_t *slab);
into struct sock *sk_alloc(int family, gfp_t priority,struct proto
*prot, int zero_it);
Kernel for Fedora Core, use the new signature from 2.6.11 kernels.

So all i want to do is to identify if it is redhat kernel or vanilla
kernel ( from kernel.org )
and looking for a macro or similar way to do it