I'd also make a point of using an extended red sensitivity film, to get the most out of using the red filter, enhancing the response to the light that does get through the filter. Strictly speaking a magenta filter will make the green darkest, but the red will do the job as well in practical terms.
Not necessarily David, Tech pan is an extended red sensitivity film without being IR. IMO these films are a pain in the a$$ to use. WIth a red filter and normal panchromatic film you should see the difference in contrast very well with the sign.
I added the part about the extended red sensitivity because I've run into some very nice pan films which were pretty poor in red sensitivity, panatomic-x is one that comes to mind. Compared to the response of ordinary Tri-x it's nearly ortho film, and the Tmax films even more sensitive.
I'd think the SFX would be perfect for this job.