Although the answer with "!" was chosen as the correct answer, this is NOT true. I´m not sure about Windows Explorer in Windows 10/8.1/8, but I am certain concerning Windows 7 and XP.
The character that moves your filename to the very top is "'" (alt+39), and second best is "-" (the minus sign).
But sorting order in Windows Explorer is more complicated - it depends on the filename-lenght also, and numbers are treated very special.
The second character (and the following) is treated different. Here you often go best with a " " (spacebar), followed by the characters mentioned above, but you´ll have to try out, because it´s not so easy to find out the exact algorithm:
Here is an example for the correct sorting order for your understanding:
Another example:
Same filelenght:
Finally the very special logic when it comes to numbers:
But nevertheless: Renaming folders or files this way, you can quickly find what you are searching for.