The information below is taken from the FAQ at
EAGLE uses and shows in the Layout Editor (also in the Schematic) a proportional font by default. But this one cant be used for generating manufacturing data by the CAM Processor.
The CAM Processor can only work with the EAGLE internal vector font. The appearance of the vector font however, differs from the proportional font in size and length.
Thus we recommend to write all texts at least those in copper layers in vector font.
Besides, there is the optionAlways vector font in theOptions/User Interfacemenu which displays and prints all texts in vector font, independent of the originally defined font. If this option is active, the texts on the screen will look exactly the same as they will do on the printed circuit board. A particularly suitable example to demonstrate the differences would be inverted text in a polygon (therefore the text is written in one of the Restrict layers).
If you pass on the BRD file directly to your Board House in order to let the operator there generate the manufacturing data, its recommended to activate the optionPersistent in this drawing, too. In this case his EAGLE system will display the vector font as it is on yours. It does not matter if the optionAlways vector font is set or not then.