Hershey fonts and substitute()

Hello R users,

I am new to R, so this may be a very stupid question. I need to 
subscript the dotted circle (Hershey escape sequence "\\SO") to a 
string. I tried using

     text(.5,.5,substitute( R[disk] == 5 R["\\SO"] ) )

but it turns out to be a syntax error.

Do you have any suggestion?

Thanks

Gaetano