I don't think there is one. Reddit has a rule that you don't post your own stuff. That would seem to prohibit any kind of "show" post.
(It's a stupid rule, I think. And your idea is a good example of why. For another, imagine such a rule on, say, YouTube. Why shouldn't a single account's Reddit posts be considered as a kind of channel?)
Feel free to post links to your own content (within reason). But if that's all you ever post, or it always seems to get voted down, take a good hard look in the mirror — you just might be a spammer. A widely used rule of thumb is the 9:1 ratio, i.e. only 1 out of every 10 of your submissions should be your own content.
Make sure you're in an appropriate subreddit and be transparent and you should be fine.
Interesting. I certainly remember such a rule. I haven't looked at the reddiquette in years. Perhaps it's changed?
In any case, I would still say that the "if that's all you ever post" note is silly. It deprives Reddit of the channel idea, which would be a good addition, I think. (If people don't like your stuff, then they can downvote it.)
I've been wasting time on reddit since it was written in Lisp, long before subreddits existed. They have always allowed reasonable self promotion. You may be remembering a rule that was put in place for a specific subreddit? Anyways, the general rule is self-submissions are OK as long as you are straightforward about it. (e.g. "This is my site, some feedback would be great..." instead of "Hey, look at this amazing site I stumbled upon")
(It's a stupid rule, I think. And your idea is a good example of why. For another, imagine such a rule on, say, YouTube. Why shouldn't a single account's Reddit posts be considered as a kind of channel?)