Hi Scotty
The crayon thing is easier than you think.
Once you have painted your scope, and it has dried sufficiently, simply get your crayon and rub it over the lettering, don't be afraid to use some pressure as you want it right into the groves.
Next you can take clean rag and start whipping the excess off, wiping to the end of the scope. You can also use a sharp craft knife to lightly scrape off excess crayon.
For even more realism, and that warn used look, take your knife tip and dig a little of the crayon out carefully so some of the letters are not quite complete.
Trust me, it's not hard, just take your time, and you will nail it.
Good luck with your build