I've personally never removed the copyright, I figured out that several spambots find you through search engines, and as such, removing that at the bottom will 'hide' your forum from search engines... Kind of...
I wanted to with phpbb 2 and "claim" it was my own, but that urge I quickly discarded when I told myself "hey, I'll really make my own, or join the phpbb team (I can't get away with my own conscience)." I couldn't get phpbb 2 to work anyways. (Check out my locked topic from years ago about how I couldn't get a unsupported, modded version of it to run on a PHP 5 server, and wanted support from here)
// I'm excellent with PHP 5+
So until I really make my own (that is if I want to, or continue to love phpbb), I'm using phpbb, and proudly showcasing it.
The best way for protecting myself from spambots was to hide my entire forum from search engines using a robots.txt files, it worked so well I was even able to remove the CAPTCHA. I do understand that this does hide new visitors from finding my site through anything but referral. It is inevitable they will find me though when my project goes public. (I know, that paragraph was off topic, I'm good at that as of late)