What about making not only the sign (which asks commuters to give up seats to those who need them more) more prominent, but also the seat? What if the seat is also painted yellow like the sign?

What about painting the wall directly behind the seat yellow also? This might help the individuals taking the seat to be more mindful to give up the seat to someone who needs it more.

Also with the colour of the seat standing out, it might just shame them into also giving up the seat.

David Edward Hester