What would be an equivalent to Q.E.D in the jargon of Halacha literature? Usually in the Gemara we something like: קא משמע לן, however I can't think of a word that is used as Q.E.D.
Maybe הלמ״מ would be a good candidate or יצתה בת קול ואמרה?
שמע מינה and קא משמע לן are used that way but both can also be used to introduce the conclusion rather than end the train of thought.
I haven't seen any research on this, but maybe דו"ק.
מאי קא משמע לן and קא משמע לן seem to fit the description provided in the Wikipedia link above.