Are Digital Signature Analyzers still used?
This kind of analyzers is a 40-years-old technology, see publications of HP in 1977-s. It was suitable for relatively primitive digital logic.
Today this is replaced by JTAG chain scan, by BIST  (built-in self test, not "Behavior Intervention Support Team"), then by ICE (in-circuit emulators), and finally with real-time full-blown on-chip logic analyzers and VISA debug interfaces. Or a combination of all the above. There are some more advanced debug tools in the works.