What signal do bg and fg send?

I know that ctrl + z changes a process from _foreground_ to _background_ - as **suspended** - through SIGTSTP. I am able to re-run that background suspended process through either fg or bg as required. **Question** * What signal do bg and fg send? Not sure if both send the same or are different. I did realise there are no neither man fg nor man bg. And well, there is no information about the signals through fg --help and bg --help