For the article you linked it references the specific start up options used by the Database Engine ("sqlservr.exe"). So the "-" dash is used as stated in the article. This article points to the method used in a DOS prompt to start SQL Server in single user mode. I believe using
/m"SQLCMD" would work the same way, but I normally use the commands noted below.
So from a DOS prompt, the command to start SQL Server default instance in single user mode and only allow SQLCMD to connect would be:
If you have a named instance it would be:
sqlservr.exe -m"SQLCMD" -s MyServer\MyInstance