Summary

Create coffee stencil with your text on it.
Use OpenSCAD 2015.03 and stencil fonts.

Instructions

Use Customizer OR:

Install stencil font, or you will be unable to use letters with isolated perimeters (O or B)
Open coffee_stencil.scad in OpenSCAD 2015.03
Edit Text variable
Set desired font name as Font variable
Adjust Spacing if needed.
Set Height of stencil (2.2mm ought to be enough to anybody)
Set diameter by changing Dia (typical values are 62mm for small cup, and 83mm for mug)
Render and export
Print with PLA (Layer height = 0.2, perimeters = 2)

Avoid exposing stencil to high temperatures (by plunging into hot coffee for example)