From page 271 of the manual
Station. Between the OSB and the box is a numeric of the station number. For example, OSB 6 will have a "7" between it and the station details box. For station 6, this numeric is displayed above the box. If the station has an error, this will be replaced by an letter failure code (H, I, P, or F).
Page 272 shows the following:
In place of the Station indicator numeric between an OSB and Weapon Station Box, a letter code may be used to indicate a failure in the station. These include:
H This would indicate a hung store.
I This would indicate a mismatch between what is specified in the profile and what is set in the inventory
P There is no profile that contains the weapon loaded on the indicated station.
F This would indicate a station fault