I think it's a fair enough comment from Peter... it had crossd my mind that my insurance co are quite up front they will not pay out on an engine where you haven't recorded serial numbers. If Jon is covered by insurance with similar clauses hope he turns up the number in his outboard manual.
I wondered if it was a general theft or targeted. Few years back our stables/outbuildings were broken into and they just pinched some ice creams from the freezer... really. They left a lcd TV, DVD player, DJ/PA gear, Zodiac packed in 2 bags, Tohatsu 9.8 and much more. Police commented that week in our area they were just targeting generators, chainsaws, petrol strimmers/hedgetrimers, quad bikes & expensive mowers.
We were very lucky because the one outbuilding they didn't look in had all those things.