As long as you are the proprietor of the business and you NOTIFY your staff that you will be monitoring the computer due to abuses this is perfectly acceptable. You own the computer, and if you want to monitor it then that is your prerogative. To remove the icon from showing permanently the only option I know of is that you need to purchase the Remote Desktop software suite from Apple and in the preferences it has an option to disable the menu icon. A temporary fix is simply to command drag the icon off the menubar like you would an application from the dock. Poof. However this is only temporary and usable for ONE active session. As soon as you disconnect and then reconnect again, the icon will reappear.
It would be nice if there was a way to permanently disable this button, but besides Remote Desktop, I don't know of one.
If you are planning to use this for nefarious means remember that it is very possible for them to turn it around and put you in some real legal trouble. Don't invade peoples personal privacy, and don't be stupid. As long as you notify them that it should be considered a public and monitored computer, you should be fine.
yes, Turn off all sharing in sharing prefernces that are on by unchecking ALL boxes. Log out and the icon should be gone in menu bar. After this is done you should be able to turn on what was turned off and the icon should still be gone, if not there is a connection to your computer.