Snapchat introduced private Stories — indicated by the purple lock symbol — to give users more control over the audience of their Snaps. Before private Stories, if you did not want someone in your Friends list to view your Story, you would have to block them on Snapchat entirely — at least until the Story expires — or send it as individual Snaps to each recipient. But private Stories allow you to create a subset of friends to which you can share Stories that the larger group won’t see.
If you see a purple lock on a friend’s Snapchat Story, that means you’re part of a select few they have chosen to be able to view that Story. The lock will be purple if you haven’t watched the story yet, and gray if you already have.
You might notice that private Stories sometimes show up as blue rings with locks, and in that case, what we’ve explained above still applies. Snapchat color-codes a Story according to the tab from which you’re viewing it. The Stories tab has a purple accent color, so new Stories that you view from there will have a purple ring. You can also view Stories from the Chat tab, and since it has a blue accent color, Stories appear with a blue ring as well.
You can make your own private Story by selecting the gray icon that says “Private Story,” which pops up in the page you’ll see after you hit the Share button on a Snap. Private Stories appear just like regular Stories do, except they have a little lock icon on them as well. Your friends won’t get a notification that you’ve created one, but rest assured that your private Story will only be seen by the friends you choose (via Snapchat).