Index on whatever tag something <b>of {index file name.cdx}</b>creates a .cdx file independent of the table, i.e. it may be open shared and even read-only. This index is not opened automatically when you use the table, so you have to open it explicitly:
use foreign_table order something of {index file name.cdx}.Signature { margin-top: 12px; color: #666666; } .Signature a { color: #666666; }