I have never, ever, seen a PHP file using hashes (#) for commenting. But today I realized that I actually can! I'm assuming there's a reason why everybody uses // instead though, so here I am.
Is there any reason, aside from personal preference, to use // rather than # for comments?
2021 UPDATE: As of PHP 8, the two characters are not the same. The sequence #[ is used for Attributes.(Thanks to i336 for the comment)
Original Answer:
The answer to the question Is there any difference between using "#" and "//" for single-line comments in PHP? is no.
There is no difference. By looking at the parsing part of PHP source code, both "#" and "//" are handled by the same code and therefore have the exact same behavior.