/etc/rc.local is execute at boot time as root. This is not the same as running something at login time.
If you want to run something in the login shell of users, put it in the /etc/profile. This is the global file which is executed in the user's [bash] shell when they log in.
See the bash manual page, FILES section to see other files which are executed and when (e.g. on logout). By the way, I am assuming you're using bash for your user's interactive shell.