Ideas for insignia

Got a friend who makes knives out of railroad ties and is now getting some etching equipment for adding names, etc. He mentioned wanting to have a personalized insignia to put on all his knives, so I'm looking for some ideas. Another friend and I talked and were thinking maybe something with his initials (T.D.) and some graphic that has something to do with the railroad because that's his day job (and night too really). Anybody got some good simple ideas good for etching? Much gratitude in advance.