Think he's talking about BLM leased land. Do'nt know about Montana, but I think Colorado just changed the law to where you need permission from lease holder.
Not on BLM land you don't, no matter the state. Posting of BLM lands by a grazing permit/lease holder is a prohibitive act by regulation and can result in the lost of their grazing priviledges. State lands is a whole different kettle of fish...