As part of the process of filing for FCC renewal of their broadcast licenses, commercial and noncommercial full power radio stations licensed to communities in the District of Columbia, Maryland, Virginia and West Virginia must begin their pre-filing announcements on April 1, 2011.  Radio stations must air these announcements at least once a day on the 1st and 16th days of April and May.  At least two of the announcements must be broadcast between 7:00 a.m. to 9:00 a.m. and/or between 4:00 p.m. to 6:00 p.m.  If the broadcast station does not operate during these hours, two of the announcements must be broadcast during the first two hours of operation. 

FM translator stations do not need to make any pre-filing announcements. 

For more information about the broadcast license renewal process, see my blog piece here.