You will probably be given a seat assignment when you check in rather than a boarding pass. Best to

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I understand florida resort hotels that LH3600 is actually a train. Can someone tell me how the ticketing for the train journey works? Do I just present my flight e-ticket to the train conductor for scanning or do I have to get the train equivalent of a "boarding pass" (e.g. a train ticket or other such document) on arrival at Frankfurt?
You will probably be given a seat assignment when you check in rather than a boarding pass. Best to go to the source with your questions rather than posting on a travel florida resort hotels board as there is not a great chance that someone who has had this experience will see this thread and can give first-hand information.
Even if the ICE trains that do not have any "R" symbols, if your are traveling during the rush hour, for example trains that get sandwiched around 4pm-7pm time slot around "R" trains, you might still want to get a seat reservation. Germans seem to be keen on reserving seats. On some ICE trains, even what I thought were at off hours, I might find just two unreserved seats in a particular car. If you hopped on an ICE without seat reservations, look at the red LED display above each seat. Even if the display shows reserved for a segment, that seat is free to use until the train reaches that reserved segment.