Searching for a Photo Theme

I think it would be neat to have something that I take a picture of everywhere I go. Not a landmark, though I'm sure there will be plenty of those, but, rather, something that would mark the difference and sameness of every place I see. For example, perhaps you remember posters of the doors of Europe? I couldn't find that one but this one of the doors of Yale is similar in concept.



That's the kind of thing I'm looking for. Some ideas I've had: mailboxes, window flower boxes, feet or hands (a stretch but I really love feet/shoes and hands), some sort of sign, rocks. Nothing's floating my boat and a lot of the destinations are really arrive, eat, sleep, and leave the next morning. So perhaps the constant is food, as is so often the case. Perhaps the dinner table each night? Ideas please!