NF_IP_POST_ROUTING hook question (2.4)

In the NF_IP_POST_ROUTING hook function, how can I
tell that packet originated locally vs was forwarded ?
I need to hook NF_IP_POST_ROUTING not NF_IP_FORWARD.

I'd expect that 'net_device *in' argument to be  not NULL for
forwarded packets.

But what I see is NULL for both forwarded  and locally sent packets
(in NF_IP_POST_ROUTING hook).
Which field of skb can  tell me that packet originated locally ?

Yakov