In Puerto Rico we say "o con acento" as well.That's a pretty natural way to say it, in my view. In Mexico at least, it's probably a little more common to say "o (or whatever vowel) con acento", instead of "tilde" [...] . I don't know how it is in other countries.
Well, we´re also been taught that "acento" is the stress you put in a syllable when you speak and "tilde" is a graphic mark of that when you write.I appreciate it! I was taught not to use the word accent when speaking of a written accent mark, but of course what is taught in classrooms doesn't always reflect what is commonly used.