When I enter a quilt in a show, I list the pattern or designer on the entry form (if it's not my own design). I've been kind of stewing about what's going on with the national modern guild and their talk of "derivatives" and the hoops you need to go through in getting permission to use a design idea. I can understand if you've obviously used a particular pattern or a readily identifiable design. But much of what I do is based on things I've seen somewhere but I'm not intentionally copying something that I can refer back to. For instance, according to the modern guild, if you place your HST's in a certain way that some designer already used, you'd have to get permission. It's enough to not want to enter shows.
I will say, though, I am irritated when I go to a show and see a quilt that is obviously a copy of something and there is no reference on the quilt's info sheet of the original designer. A few months ago there was a quilt with cute little birdies that was from a birdie-a-month thing I saw on a blog. There was no mention of the blog. I'm sure that the person who made the quilt knew the blog since they used it every month for their birdie block.