Do you see this if you start Emacs using
emacs -Q? If not then bisect your init file to find the culprit.
That should always be the first step when trying to investigate some problem or something you wonder about: find out whether the problem comes from Emacs or yourself -- i.e., code that you have, one way or another, added to Emacs.
I think you are using some code (other than what comes with
emacs -Q) that does this. Vanilla Emacs (
emacs -Q) does not do it. For one thing, there is no predefined mark
M. Likewise, there is no predefined
??. And that's really both a
? mark, in the mark position, plus a second
? after that position.
To remove the marks (however they were created), did you try
<M-backspace>) followed by
RET? That's command
dired-unmark-all-files, and a simple
RET at the prompt removes all marks, of any kind. That should include the mysterious