are there any specific features that stability augmentation systems have in a helicopter compared to an airplanes?
To answer the specific question:
A panel, with a SAS ON/OFF button. A Force Trim switch, so that the SAS and autopilot are permitted to control the cyclic, pedals, and collective.
If joined to an autopilot, an ALT button, HDG button, YAW button, VS (vertical speed)button and some more things to play with if it a 4-axis setup, connected to FMS and so on.