Update (28 Jan 2017) Changed the default font and added more options.

The original font was a mono-space font and looks kinda bad. I changed the default to a san-serif, and made it configurable.

I've also made the hole size configurable. If you find it unnecessarily large (...which it often is), you can now change it.

Pro-tip: Pause the print when it is halfway done and change to a different color filament. The contrast will make the text much more readable. You can easily pause the print and move the head out of the way using pronterface, change filament, then resume print (...need not bring the head back into position, pronterface will take care of that).

A very simple and customizable key tag, suitable for both one or two lines of text.

Unfortunately, OpenSCAD do not provide any means to determine the text dimension, so you may need to manually adjust the text/tag size to make it fit.

Disclaimer: I do not own a Tesla S.