You can also get special "anti-theft-paint" to match your boat's paint
scheme. It comes in spray cans from your local auto parts or hardware
store, in thousands of colors. I also etch each major component (block,
lower unit, cowl) in visible, and if possible hidden locations with "Stolen
From ...town, state, phone number..."

If you give a thief a choice between a shiny new motor, with original mfrs'
graphics, and a badly painted, unique motor, with contact info permanently
inscribed, which will he take?

This may be a dumb question, but when I buy my boat, I'm planning on
storing in an open lot. Obviously, I'm concerned about theft. It
would seem to me that removing an outboard motor is probably not too
hard to do. Is there some kind of locking mechanism that helps
prevent theft?

I just use a padlock though the holes in the mounting clamps.