Thanks, gents. I was pretty happy with this idea, but my sewing skills are pretty lacking...so I had to lean on my wife for her sewing abilities.
Did she hand stitch it, so it goes through just one layer of the twill? Or stitch it (either machine or hand) so it goes through both. I love the idea, I will totally be copying it, but I prefer using my sewing machine and would hate to but stitches through the outside of the flap unnecessarily.
She hand stitched it so that it wouldn't go through the top layer. Filson bags are supposed to look rough and relatively ragged, but stitching through the top just would've bad, imho.
For those interested, here is the font that I used and here is the printable fabric that I used. I tried printing on my standard inkjet, and the text ended up looking pretty bad...so I then used my photo printer, which resulted in perfectly clean text. Also, if you want to get it close to the color of the tag, you'll want to add a layer of almost pinkish-yellow underneath the text to give it that off-white look that exists on the actual Filson tag. Certainly doesn't matter in the end, but given I spent a while trying to match the font/layout, I figured it wouldn't hurt.
Hope that helps.