I secure my 6hp with a "slot lock " over the clamp screws. I have also threaded a length of hardened chain between the exhaust housing and the swivel bracket assembly which a I padlock around one of the "pushpit" legs.
I'd not rely on a padlock through the clamp screw handles
The weak part in any such security system is the padlock.
Some cheap locks are so poor that you can easily saw through the hasp so good quality locks are needed and "disc locks" that don't have shoulders that can be hit with a hammer are probably a good choice
If criminals are determined enough they will chain saw the transom off your boat complete with outboard.so ultimatly you cannot win .
Marking the outboard with your zip code is also a good idea.