Placing a wet umbrella on an empty adjacent seat. Hey, when’s the last time you enjoyed planting your behind in a huge puddle of cold water? For optimum bus citizenship, shake off your umbrella before entering the vehicle and then store it under your feet or in your bus chick bag* for the ride.
*I have lost many an umbrella by leaving them on the floor, so I now always put them back in my bag. My current bag has a mesh outer pouch that seems to be made expressly for this purpose, but if you don’t have one, you can carry a plastic bag or umbrella cover to avoid getting your other stuff wet.