iv'e had this type of question in the past and Visteonguy was able to help me out. i'll try to explain breily what he has passed on to me. i have yet to try it but the understanding is there.
he makes raised letters all the time for his signs. he uses an end mill to route around his letters so it knocks out all the wood around your letter so it looks raised. im trying to find the thread he posted awhile back of the signs he made but i can't find it, i'll keep looking though. but he is definately the guy to ask on this!!!!!!
not sure what you have but you might want to look into a trim router for this. (homier.com has them for i think 10 bucks, (thats what i got mine for. the shipping time is awesome. i ordered mine on a friday and got it monday.)
hope i can get you going in the right direction.