Hi,
In T-Code FBKP' you maintain different parameters for Automatic Posting, Special GL Indicator, Field Status Variants, etc. Now if you select the Special GL Indicator , under that many indicators would be there under that for each indicator the posting key to be assigned in mentioned. Generally in standard posting key 29 & 39 are only used. 'F' is coming as in the Special GL indicator the Target Sp GL Indicator would be set as 'F'. To have a bifurcation of normal entries and special entries, Special GL indicator concept is used. Values posted through Special GL indicator doesn't go to the Reconciliation GL as maintained in the Vendor or Customer Master, but the posting goes to the Additional GL which is assigned against a Reconciliation Account.
Regards,
Malhar.