It's a "canopy latch safety catch" added as an option to earlier RV-12s to temporarily hold the canopy in a semi-opened position while the aircraft is at rest or taxiing. It's intent is to hopefully preventing the canopy from suddenly being blown open by a wind gust from behind -- such an event could cause the canopy to blow excessively open, break the retaining struts, fall forward into the prop, and generate very expensive noises.