I think the top two kanji say 清次 (Kiyotsugu) which would be the smith's name, but part of the 清 kanji is removed due to the opening of the peg holes, which is not uncommon. The bottom two kanji are something that was scratched on later, and I think they have no relation to Kiyotsugu, and they may not even be written by a Japanese person because they don't make sense. Just some scratches that maybe someone etched on the tang for who-knows-what reason.
There were several swordsmiths who signed using the name Kiyotsugu, spanning from the 1200s all the way to the 1940s. This would (supposedly) be one of the older ones, maybe pre-1600, but its hard to say. Could also be a fake signature put on a mediocre blade in order to make it more appealing to buyers. This is something that is very common. I don't mean the signature was added recently - it could have been added in the 1800s in order to make the blade look more interesting.
I'd say the blade itself is circa 1600s. The quasi-military mounts were probably made during the war, so that the owner could take it off to war with him. The nasty opening running the length of the blade isn't a good sign. You might try sending it to the Nihonto Message Board for more info.