When you click the 'share' button beneath a post on MathOverflow, a box pops up containing a short URL for the post, e.g. of the form
Unless you have been reading the (contentious, at times) thread "Privacy of software-generated links to questions and answers", you may not realize that this URL identifies you. In particular, the trailing '3' in the example above is my user number, and my identity can be found by entering the URL https://mathoverflow.net/users/3.
Stack Exchange staff: Can we please remove the trailing user number from the URL generated in the 'share' box, on MathOverflow?
Notably the 'share' link is the most accessible way to obtain a URL direct to an answer (as opposed to a question). The 'cite' link also provides a URL, with no personally identifying information, but it is slightly less obvious to extract.
There is an existing long discussion of this issue, sadly at times generating more heat than light, at the above mentioned thread. I will quickly recap the pros and cons of the trailing user identifier here.
Pro: the "announcer" badge rewards people who bring attention to StackExchange hosted threads, by posting these links in other fora. The trailing user id is used to track the number of visits due to a particular user.
At least some of our users are discomfited by this personally identifying data being surreptitiously embedded in a URL.
It is conceivable, although there is no known case of this occurring, that this personally identifying information could break the expected anonymity of mathematical refereeing. It is certainly very plausible that a referee will at some point (and likely this has already happened many times) want to tell authors about a post on MathOverflow relevant to the refereed paper. If the referee uses the URL generated from the 'share' link, they will accidentally reveal their identity. It is unreasonable to expect that users of this URL are aware that it may reveal their identity.
Discussion: Personally, I couldn't care less about the Announcer badge (and I think the other moderators, and much of the community, agree). I am not comfortable with MathOverflow revealing personal information in an unusual way that discomfits some of our users. I am quite concerned about the potential (admittedly hypothetical) impact on a referee.