When the movie "My Big Fat Greek Wedding" came out several years ago, the title was printed on posters as "MY BIG FAT GRΣΣK WEDDING", with the capital letter for sigma in place of the Es. The purpose was, of course, to give a "Greek" look to the publicity material, but for me and I assume many others who know a bit of Greek, it read distractingly as "GRSSK". I saw the same phenomenon recently in promotions of the movie "Borat", which appears as "BORДT" with a Cyrillic D in place of the English A. This one was less irritating to me since I don't read Russian, but I wonder if those who do thought "BORDT" every time they saw it.
I find such substitutions rather linguacentric, since I believe it unlikely that anyone with a knowledge of both languages would ever think of mixing them in that way. One has to view the sigma or the Cyrillic D as a graphic or a symbol rather than a letter for it not to be distracting. I'm once again reminded of the Stroop effect and a question posed by my classmate in the psychology/linguistics class where I first learned of it: "Would it be confusing if the color words were in a different language that you didn't understand?" Of course not!
I was plodding through a highly technical paper at work recently when I discovered, to my dismay, that the author had used both versions of the Greek lowercase phi (φ and ϕ) to represent unique quantities. Fortunately, they were distinct enough as not to be terribly confusing, but I thought it would be difficult if I ever had to discuss the equations out loud. After all, using the two phis is equivalent to using both forms of the English lowercase "a", and one would have to refer to "loopy phi" or "straight phi" or something like that to distinguish them. Yikes!