Icon theme was changed at 6.1 to Colibre. The prior Tango theme is still available if you prefer (Tools → Options → View: Icon Style)
Indicator of unsaved document appears on the Standard toolbar Save split button, and also in the Status bar adjacent to the zoom and document view attributes. Both the toolbar button and the the Status bar element will respond to changed icon theme presenting different design in Colibre, Tango, Breeze, Sifr. At the 6.2.0 release you’ll have the new Karasa Jaga icon theme as well.
Default is now Colibre, but pick one you like that meets your needs.