Theory: somebody wrote up the advertisement in MS-Word (which auto-corrected a double-hyphen into an em-dash), copy/pasted it into a web form (with the paste preserving the Unicode character), submitted it to a website that lets you add advertisements to BART reader boards, the browser converted the Unicode in the textarea to utf-8... then the stupid cgi script blindly took it and passed it off to the reader board, which only knows iso_8859-1/Latin-1, and not utf-8, because it was built so long ago.
But I stilllllll love tech-nol-ogyyyyyyy....
... but noooooooot as much as-you-you-see.....