[R] Plotmath issue superscript "-"

[Scionforbai]

Hallo,

> If you need a subscript as well, I like
>
>   plot(0, main=quote({NO^'\x96'}[3]))


I tried this but I get:

>  plot(0, main=quote({NO^'\x96'}[3]))
Errore in title(...) : stringa multibyte non valida ('invalid multibyte string')

My R version is:
platform       i686-redhat-linux-gnu
version.string R version 2.4.1 (2006-12-18)

locale is: LANG=it_IT.UTF-8

What is this multibyte string? Does it depend on LOCALE settings?
Where can I find further docs on this way to pass character
descriptors?
Thanks,
ScionForbai