It appears to just be restating what we already know and practice: no unbagged bikes allowed on the train, folding bikes should be folded and bagged in a bike bag, non-folding bikes should be disassembled and then bagged.
My Japanese is not that good, but I think the poster just politely asks bicycle riders not to ride in trains and to dismount. When dismounted, it is of course unavoidable to bump from time to time into other passengers, in particular during the rush hours.
I just saw the same sign in front of Iidabashi Station along the Sobu-sen (JR) this morning. Maybe this is part of a new JR campaign, especially since we are heading into the summer months and it might have something to do with the recent "自転車ブーム". In other words, a lot more people with bikes going places.
I know there are places in Japan (very rural that is) where you can bring your bike on the train with no disassembly required!:clap: