I have the same problem. I am entry number 74. I found my HIN on the stern but it is mostly obscured by paint
. I have had an engraving shop make me a metal plaque that I will pop rivet/glue to the starboard side of the hull
just below the cap rail. That is how the HIN is displayed on Bavaria
yachts. Since I have paper documentation
showing my HIN I don't see why the plaque wouldn't be OK. I'm sure the Mexican authorities just want to be able to see a number on your boat that matches what you put on the TIP. I doubt they care what it looks like. From what I read it seems some boats were impounded because the HIN could not be easily seen so making it obvious might make everyone happy.
PS: I have a windvane
on the stern which adds to the impossibility of seeing the original HIN.