Choose a robot from any avenue of entertainment media, whether it is a film, cartoon, comic or other. Tattoo the full image of the robot or a simple bust if you are not willing to donate a large amount of skin to the cause. You are free to use any color scheme you want, but it may be best to use the exact colors used for the actual robot. For instance, C3PO from Star Wars should be gold in order to be true to the character.
A robotic cross section is a patch of skin that is tattooed to resemble the image of a circuit board operating just beneath your skin. The wires and computer chips can appear functional or shorting out with cheap duct tape binding certain wires together or even a band aid to add a certain comedic value. The cross section patch can also be any size you desire, though you should consider an area large enough for viewers to determine the concept for the piece.
A robotic script can be anything from binary code to actual letters designed to appear robotic. Binary code is a system of 1's and 0's set in a particular order to represent particular words. You can find binary generator and translator online or in books, or just tattoo a random set. Script that appears robotic would be the basic letter of the alphabet, designed to look like bolted metal or intersecting wires. The words themselves are entirely up to you.
If you are seeking a robot tattoo design that is unique and one of a kind, you can draw the robot yourself. Just determine the appropriate size for the tattoo and draw a robot fitting with that size. If you are not comfortable with your artistic abilities, you can employ a tattoo artist to design it and simply instruct him on some or all of the details. The image of the robot can be as extravagant or as simple as you want, reflecting the appearance of an individual or just the stereotypical box robot.