You should include in your game (perhaps in the response to the HELP command) something saying that you own the copyright on the game, and giving a distribution policy: for example, you may not want it to be distributed for charge, you may not want it distributed at all, or you may not care.
On a somewhat related topic, you should ask John Francis (jfrancis@dungeon.engr.sgi.com) to list you in the file /if-archive/info/author-list.txt at the IF-Archive. You can give him your email address and the distributability status of your game or other IF product.)
On another somewhat related topic, getting commercially sold games, even if they are no longer available, for free is illegal unless the copyright owner has specifically decided to allow distribution. There is no such thing as "abandonware": just because a game or program is no longer sold does not make it legal for you to distribute it. On the other hand, most people are in favor of getting copyright owners to freely distribute abandoned programs, but that choice is up to the owner. This specifically covers most of the Infocom games, but see [Where can I find Infocom games?: 6.7] for more information on that.