Here's a thought, and this just might be the answer everyone has been looking for.
Perhaps, if someone gets on a bus and there are no empty seats, and for whatever reason (carrying a baby, hidden disability, WHATEVER) would really like to/need to/have to sit down, instead of assuming someone should just KNOW that they need to sit down, maybe they can cast their eye about, approach a likely looking person (I would suggest a male between the ages of 25 and 60), and sweetly, with a humble face and a self deprecating way about them, ASK if they might sit in their seat. Heck, they might even want to TELL them why they'd like to sit there (the baby is so heavy, I just had a hip replaced, I fainted twice today in line for TSM, etc.).
Then, and I'm going out on a limb here, the person being ASKED can gallantly rise to their feet and allow the now graciously appreciative asker to sit. OR, if the person being asked has a reason they don't want to give up their seat, they can politely say 'gosh, I'd love to help, but I'm exhausted/I just had my hip replaced/my mommy told me not to talk to strangers'. At which point the person doing the asking can say something along the lines of 'oh, goodness, I totally understand', which allows a nearby Good Samaritan the opportunity to offer up their seat, OR it allows the original asker to stand graciously, withough glaring at anyone or feeling put upon, and take that moment to reflect on their good fortune that this is the problem they have to deal with, not famine, flood or pestilance.
There now - wasn't that lovely??
KC