Vectric's V-CarvePro software is highly capable of what you require...! It has the ability to v-carve enclosed vector font types OR engrave single line fonts. The only issue is tooling. Most likely... for lettering at 3/8" you'll be using 30 or 60 deg (included angle) engraving bits for enclosed vector alphanumerics... and for the single line font engraving... something in the 0.0625" to 0.125" neighborhood for end mills... ballnose or otherwise.
Hope that helps...
Senna
aka BOOMER52 >>> http://www.rcgroups.com/forums/member.php?u=159693