Well, on the bright side, looks like you have a couple of pieces to practice with.
I've never routed letters, on anything, but have routed some edges on red oak. I'd say go very, very, slowly - not the bit, but moving the router. Not sure that would do it, but all I can come up with at the moment. Or, perhaps a Dremel would work better, if you have one.
Does it 'have' to be routed? Or could it be burned?
Theo, I can't burn. Never could. Tried & tried & tried. Just can't get the technique of it.
I had to use my Dremel on the Walnut portion of this to do some of the lettering because my router (trim or otherwise) just wasn't gonna do it. I tried using my Dremel on this, but that was just as bad; I tried going super slow, I tried doing it in multiple passes, I tried slower rpm's, maxing out the rpm's... I can't TELL
you how disappointed in this one I am... never thought I would have to give it up to the wood. I thought at first that the first piece was too dry, that the second would be a little more giving, but I was wrong there, as well. I'm thinking if I could burn, that would be the better way to go with this one; unless of course he wanted to use a light colored filling on the lettering, of course. I think on the Walnut portion we were gonna fill it in with my colored wood filler. The problem with that is that it's gonna show every single boo boo in the design.
The lesson here, boys n' girls is Walnut & Read Oak Don't Like To Be Graffitied Upon