@codinghorror @sam Thanks both for humoring this. It’s a testament to the team that something which has been one way for so long, can be openly discussed in this manner and a change be tested out in the open.
Even if this isn’t the final incarnation, I’m really happy to see how this topic has progressed, and hear from so many others on the topic.
I’m actually finding this very jarring to discern between a closed topic and an unlisted one. The icon makes sense but in the topic list where it’s so small, it’s very very hard to quickly tell the difference. This might be a bit of a case of you moved my 
but at the same time, icons should be quick to recognize.
If I may… Were your users confused because it was a padlock, or because it was similar to the closed topic icon? I think that’s two very different things.
Is that your or their feeling?
For what it’s worth, my client (single, isolated opinion from a random discourse owner) was confused by the locked icon on the private categories without associating them to the locked topics, which he didn’t see any from what I know (his forum wasn’t even publicly launched).
So, what’s the start issue? The private category icon alone that might be confusing, or the fact that two different features share the same icon? 
Both actually, closed and secure have different meanings.
Using a padlock to mean both ‘you can no longer respond to this’ and ‘you can reply to this but not everyone can see it’ is really confusing, particularly now that categories no longer occupy a dedicated column and are instead shown below the topic title.
Yes, I have already heard that one and agreed. I can cope for now. I just think it is weird that the glyph is not solid compared to all other actions.
Just added an update to add a plus to the generic comment icon, I liked the bottom corner version… but it doesn’t work as well when it’s small (in the menus)
The good news is that normal users never see the unlisted icon anyway (not that we want to make things harder for admins)…
an alternative could be trying a filled-in icon?
As suggested by myself, you could try that. I think it will then be more distinguishable.
As long as it makes sense with the other UI elements we use. It might be a good option. Filled in also signifies more weight, and a closed topic is pretty weighty when coming to UX.
I’m really glad that we’re tackling this issue. 
It was one of the first on my personal list of visual annoyances – every single time I saw a topic on the Latest list from a private category, it made me think that topic is closed. It took a good couple of weeks to “train” my eyes to catch the difference when visually scanning the list.
Anyway, one of the issues with the new icon is (as @ondrej noticed) that while the previous one was a quite large solid block, the new one is just an outline. This doesn’t fit most of the other icons used throughout the app (although we’re not entirely consistent there, yet). (edit: @awesomerobot yeah, the filled-in one looks better, though its legibility could probably still be improved)
The other issue is that we already use almost exactly the same icon for “quote whole post” button in the composer. So we’re trading multiple meanings of the lock icon for multiple meanings of the speech bubble icon. 
Please imagine close topic is new glyph. Don’t you think there is way to many similar looking glyphs if we were to make close topic solid?
Sorry about being so negative
It is very hard to tell what the icon is when it is tiny, especially on dark themes and mobile.
vs
The glyph not being full means it is a lot easier just to mistake it for text or visual glitch.
I think the filled in one is going to be a lot better.
I know it’s only been a couple days, hot take: “Have I been muting stuff on accident?”
So, um… any non-admins wanna join in the conversation? Surely someone doesn’t see all the admin icons everywhere.
So the slash is a little unclear at small sizes, especially if it’s coupled with the eye-slash… so what about a comment-x?
This also allows the icon to be a little bit larger
https://github.com/discourse/discourse/commit/9f52997be166a0c14d082274a2da5eff541435a2
Yes, we’re going with interior glyphs and I think this might be the final change? (Does everyone see why I flippin’ hate bikeshed topics now?)
That being said, I do feel the new glyph is visually superior at explains the “closing = no more replies” logic and for those that were bugged by it (I wasn’t) it discriminates between the security padlocks seen elsewhere. Here’s another sample 
I can’t easily tell apart the two icons above. The x and the + look very similar. 
I don’t think it actually matters here, inside the topic? Opened is always accompanied by text.
Maybe… it still looks odd to have two very similar icons that are supposed to convey diametrically opposite meanings.
People usually call the action “closing a topic” or “locking a topic”, not “declaring that no more replies shall happen in a topic”. 
