[Sangetsu]

Swords were often kept in storage (temples and such) for safe keeping, and these tags were attached so that the owner could be identified.

The ownership information is not important, all swords were forbidden and confiscated after the Japanese surrender at the end of the war. The Japanese were by then sick of war and militarism, and gave them up willingly, for the most part.

The information that is important would be found on the tang of the sword. Drive out the bamboo peg holding on the hilt, and remove the hilt. The majority of swords will have a makers mark engraved on the tang, and these marks often include a date "made on a lucky day in such-and-such" etc.

If the tank is too rusty to read the signature, don't try to scrape or brush it off, put a piece of paper over the tang and rub a pencil across the paper to get a relief of the signature.

Most Japanese swords have some kind of value, depending on the condition. If it's very rusty, is bent, or has a badly chipped blade, it's not going to be worth very much. On the other hand, someone went to the trouble of having it stored in a safe place, so it either has intrinsic value, or had personal value to someone at one time.

I once found a 14th century sword in America which had been beaten pretty much to death. What had been a sword which was worth at least 5 figures was made worthless. I bought it for $300 for the hand guard and fittings, which were all that had any remaining value.