I don't know why, but I like that this was a Show HN. I was just thinking, "Hmmm...creating something that is both random and memorable seems hard. That venn diagram must not intersect often."
Then I realized some of the most memorable things in my head were because they were so novel, weird and essentially random.
I know the answer to a riddle like this is something like 1Password...but it doesn't feel right, does it? The trouble might be that we're looking for an elegant solution. To me, that's always a warning sign. The search for elegant solutions tend to be fool's errands for young designers of systems.
Not that I think you were thinking this hard about it. It seems like you're just starting a dialogue, which is great.