I'm with both of you on this. I sent a PM to Andrew just yesterday to see if he could help. I suspect it is held on with an adhesive, and depending on what was used, it may or may not be removable without heroic efforts.
The problem with masking comes in when the problem is beyond a light sanding and recoating. Our varnish has broken down at the lower left corner, where water tends to collect a bit, to the point that the unit needs total stripping. Not only the strippers but also any of the more potent teak cleaners can damage the fibreglass.
Keeping on top of varnish is the real solution. One has to be sure not to let it break down to the point of requiring stripping. Here in the south, 3 or 4 coats of varnish on exterior teak will break down to bare wood on the more exposed surfaces in well under a year. That means a light sanding once or twice a year and new layer of varnish. On our last two boats, which had teak in abundance, we switched to Marine Cetol. It is not as pretty as a good varnish job and is softer so it does not take wear as well. But once you have 4 or 5 coats built up, if you don't walk on or drag lines across an area repeatedly, it lasts a year without breaking down. Then a light sanding and recoat buys you another.
Of course, the other option is "ocean gray" but especially in fresh water that tends to be "lake black". The wood also gets grainy and repeated attempts to clean it will wear it away significantly over several years.
Teak is gorgeous stuff, but just as work is the bane of the drinking class, teak is the bane of the recreational sailor.