That's funny, I never thought it was snarky, but now that you mention it I can see how it might be interpreted as such. Passive aggressive in a way, but I never thought of it like that. Thanks for the alternate interpretation!
But also in all fairness I'm paraphrasing, I can't recall the exact wording so it may well have been formulated much better than I make it seem.
Now, imagine guests being offended and not coming back to the hotel and leaving negative reviews out of spite, even if they didn't have any intention of stealing the robe.
That would make the hotel staff less snarky and rude, and more mindful about what they write on notes to guests...
Because this is the rude equivalent of the store clerk following around the aisles assuming you're a thief. A high end hotel for the rich would never dream of writing something like this -- at least not in the good days before the race to the bottom.