Notation for ending proofs It is a known fact that mathematicians use $\square$, or $q.e.d$ to end a proof of a Theorem. 
Just out of curiosity: do you guys also use these notations for other results like Lemmas, Proposition and etc.?
 A: My personal preference is to use it whenever something has a proof that lives in a block like
Proof

argument here

$\square$

By  default the proof environment in the American Mathematical Society $\LaTeX$ style  ends with a halmos.
A: I am using $\square$ behind all of the above mentioned. It is a nice way to differ writen text from proofs.
A: Yes. The open square $\square$ to end the proof of any named or numbered result, major or minor, is standard style, and has been so for many years. At one time, a filled square was popular. But this is unsightly, especially when there is more than one on a page.
It is useful to have an eye-catching marker for the end of a proof, as then the reader can tell at a glance from the outset whether she is going to face a long or short proof. For this reason, I prefer to place it on the right-hand margin, rather than as extra punctuation (after a one-em space) on the last line of text. If the last item of the proof is a (right-)numbered displayed equation, then the marker should go at the end of the next (empty) line
