Ya know, strangely, I think there's probably actually some validity to that. I know if you write on a bathroom mirror with shaving cream, even after you've cleaned it off, the mirror won't steam up in those areas for quite some time (don't ask how I know this...
![Emot LOL](images/smilies/emot-LOL.gif)
).... But I'd still be concerned about it damaging the visor. Hmmm........