- If a question is closed as a duplicate, its title will be rendered as
Original Title [duplicate].
- If a question is closed (not as a duplicate) within the last five days, its title will be rendered as
Original Title [on hold]. If it was closed (not as a duplicate, again) more than 5 days earlier, its title will be rendered as
Original Title [closed].
- If a question is migrated to another site, its title will be rendered as
Original Title [migrated]
- If a question was migrated from another site and subsequently closed for any reason, its title will be rendered as
Original Title [migrated] in search results only.
Note that the above rules only apply to the website (including the mobile site), not the mobile apps. On the mobile apps, no title modifications are performed when viewing the question, only in question lists. There, the first three above rules apply, in addition to the following ones:
- If the question is protected, its title will be rendered as
Original Title [protected].
- If the question is locked, its title will be rendered as
Original Title [locked].
Additionally, in both the app and the website:
- Tags using
[tag] notation are automatically stripped from titles.
- Exclamation marks at the end of titles are converted into question marks.
- "Straight quotes" in question titles are converted into “smart quotes”.
- The sequence "--" is converted into an em dash ("—") in question titles. To force it to display as "--", put an invisible character in between the two dashes, like in the following sequence:
- Greetings are removed automatically from both questions and answers before they are posted.
- Internal links to questions are converted into links as the title of the question. For example
https://meta.stackexchange.com/questions/97524/list-of-reasons-for-automatic-system-content-modification gets converted into List of Reasons for Automatic System Content Modification.
- In comments containing @replies to the post owner, the @reply will be removed from the comment text if it is at the beginning of the comment and the author has not commented, as it is not needed (the post owner is always notified of comments on their post).
- When a question is closed as a duplicate, any comments on the question beginning with "possible duplicate of" and containing a single URL that points to the closed-as-duplicate-of question are automatically removed at the time of close.2
Information above is taken from: Recent feature changes to Stack Exchange.
1 This applies even if the user posting the answer doesn't have enough reputation to post comments.
2 New duplicate comment rule taken from Automatic removal of comments when a question gets closed as “exact duplicate”