Your last photo shows the safety, the bar that is just below the firing pin on the face of the hammer.
When the hammer is drawn back to the first notch, the safery notch, the trigger sear pushes up a rod inside the hammer, pivoting this bar down so that it impinges between the hammer face and frame. Like the Ruger transfer bar, you don't "do" anythiong to engage it, other than placing the hammer in this position.
I believe Skeeter Skelton tested this by placing a live (or blank) round under the hammer and engaging the safety. He then used a wooden hammer handle to strike the hammer spur repeatedly trying to fire the round. It didn't fire.
Here are two of my Ubertis. The one on the left has the hammer block safety: