While it would be quick to dismiss this solicitous warning, seemingly caring for the warmer, as one of those quaint mistranslations, I believe the fault here is not with the Translation Department of the Shinkansen Trains in Japan but that the English word 'for' implies too much, being a destination and a 'on behalf' of word, as well as a word of agency. All this would be much clearer in Spanish, where the nifty 'para' could fit in. The slightly odder thing about this is that the heater is not in any way apparent. But perhaps that is what it means, Care on behalf of the missing heater.