The file information utility, ctinfo, displays index compression modes as included in the key type when displaying index information.
Example
IIDX #2 {
/* key length */ 4,
/* key type */ 2048, (0x0800 = KTYP_KEYCOMPSRLE)
/* duplicate flag */ 0,
/* null key flag */ 0,
/* empty character */ 0,
/* number of segments */ 1,
/* r-tree symbolic index */ cm_custnumb_idx,
/* alternate index name */ 0000000000000000,
/* alternate collating seq */ 0000000000000000,
/* alternate pad byte */ 0000000000000000,
};