My guild is looking to try raiding a little different when January rolls around here.

I was wondering (I really haven't looked too deep into this) if there was a way to do sign ups on the calendar by rank? I know you can do by role and class, which is great, but I was hoping maybe for some sort of mark letting me know when I do a roster that they are either a raider or casual guild member.

Any ideas?

There isn't.
What is it that you want to do? Are you looking for a way to approve people with a priority over others? If so then check out the A-TEAM status on a characters profile. Admittedly I don't know all the caveats of that system but I know others used it as a way to control auto approvals of Raider rank members and officers over trial members and such.

Ah, good call! Completely forgot about that feature. But yeah, that's what I'm trying to do, so the casuals don't sign up and get priority over a raider. Thanks!