Is the 'priority seating for persons with disabilities' sign supposed to be some sort of ironic comment? Or is that just me reading too much into it?

No answer, please. Any work of art (like any joke) that must be explained has failed.

Actually, anyone can sit anywhere. They put up signs in all public transportations. Again, anyone can sit there. Till 50 years ago, if a black man would have sat in in that exact place, you would have made the same comment. Till 80 years ago, if you would have seen a white woman (or any other woman)sit in that exact place you would have made the exact same comment. A couple (to be exact around 2006) years ago, if a Jew would have seen a 'convert' (Christian) sit in that exact same place, he would have said that exact same thing you said. To come up with jokes as such are only a matte rof ignorance. Thats all.

To tell you the truth, I am not even a woman, nor a Muslim. Yet, when I travelled the world, I saw how much freedom they had being clothed than m own mother, sister, wife and now my daughter do being half naked.