R Hunter - hi, while working in US government security, we used to see lots of outward opening doors with exposed hinges that needed the hinge pins secured. There's two ways to do this, and the solution you choose depends on whether or not you may need to remove the door easily.
First - you can spot-weld the top of the hinge pin to the hinge itself. You'll have to only do so in one spot, to allow the hinge pint to rotate with the hinge as the door opens/closes. Obviously, once you do this, you'd have to pull the entire hinge out from the door frame, or off the door, to remove the door in the future. One drawback to this is that a determined burglar could simply saw through the spot weld, given enough time and access. (For instance, if the home's not occupied full-time...)
Second - you can drill a hole through the hinge, into (but not through) the hinge pin, and insert a set screw. You'd open the door and mark the spot for drilling so that it can't be accessed while the door is closed. You'd drill the hole and you'd probably have to remove the hinge pin & set it in a vise to drill & tap the hole in the hinge pin. When you insert the set screw, you'd drive it in until it's flush with the surface of the hinge. That way, you should be able to open and close the door without scratching anything. It also won't damage the set screw head so you can extract it when you want to remove the door by removing the hinge pins.
We'd always recommend either of these treatments be done to the top and bottom hinges on a door. I'd think a good locksmith could do the set screw method for you if you don't have the tools (tap & die set) to take it on yourself. Also, you may want to find an old scrap hinge & pin to experiment with. I hope this helps you some - regards! Jim D/Heathsville, VA