The sysindices system catalog

The sysindices system catalog stores information about indexes, including R-tree indexes.

Some of the columns of the sysindices table include:
idxname
The name of the index.
tabid
The unique identifier of the indexed table.
amid
The unique identifier of the access method used to create the index. This is a join column with the sysams table.

Because DB-Access provides information about the indexes that exist for a particular table, you do not have to query the sysindices table directly.