One thing I noticed with a previous website I was associated with, if a player signed up for a raid and checked the box stating he might be late, after signups closed for that event there was no real way to see he had checked the "late" box. Is there any way to implement a notice when signups close? Either through a Private Message/Forum Post being generated to all the officers or by some other visual means on the signup sheet?

Here is a small work around.
When you view an event hat is closed or is in progress click on drop down list and select "Players who signed up (Sorted by Time)". That will show a table and the late notes will be to the right of each signup.