Sportco used to market Martini Cadets converted from .310 to .22 RF, .22 Hornet and .25/20

As part of the conversion they added a safety button that mounted on the trigger guard behind the trigger and moved from right to left on a detent. Quite nicely made.

Scroll down for an image:
http://www.rifleman.org.uk/Sportco_Martini_rifle.htm