It explained in either Ch.1 or 2 that the '007' came to be due to the boss liking the number that's why it was added on.
if you're asking why the manga is named keishichou tokuhanka 007 it's because the detective agency is named that... if you're asking why the detective agency is named that... idk lol
I believe in English it could be Special Police-unit 007. 007 is a reverence to James Bond, because the guy starting the unit is a fan. That's why when they introduce themselves, people tend to laugh or not take them seriously. ╮(￣▽￣)╭
After all that trouble to read for a long time... I still dont know why is it named "keishichou tokuhanka" especially that '007' thingy XD ┑(￣Д ￣)┍ (￣∇￣")