According to this page since August 2014, signatures don't apply in flow, but there are plans for a "Preferred name". Is this feature planned for the near future?
Topic on Talk:Structured Discussions
Is there any way to customize the name appearing at the top of one's messages?
It is not posible to customize it for the moment.
I like the proposal of DannyH in this phabricator ticket. It's adding a plain text in parenthesis after your name that can be changed anytime, and the change applies everywhere.
I see there are some details to be resolved. But starting with a global preference of "Display name" seems like a good start (mentions by display name can be implemented later). Wether to use the old "real name" field is the only thing that we've to see, but I don't know the technicalities.
Have multiple names displayed may lead to some confusion for the users, especially when you want to mention them. Which name is supposed to be used? You may have seen cases where the username is different from the signature. It is confusing as well. So this topic have to be considered carefully.
However, there is no clear plan for signatures in Flow's roadmap. It is not planed to work on this feature now.