Not as rare as this “Why?” cloud from 2002, taken from a sailboat somewhere in the Bahamas. This is completely un-doctored (in fact, the yellow tint is from me taking the photo through my sunglasses).

I was taking pictures of these “Jesus” clouds (making the obligatory high-pitched “Ahhhhhhhhh” sound while doing it) when the question mark appeared and disappeared fairly quickly (the photo before and after in succession do not have this particular punctuation).