Locks the selected layer.  
Locking a layer prevents any and all changes from being reflected on the locked layer’s content To lock a layer navigate to the layer settings menu by tapping on the settings icon of your layer thumbnail on the Layer Panel. From the settings menu, simply toggle the Lock Layer switch on. A small padlock icon on your layer thumbnail on the Layers Panel indicates that the Lock layer option is enabled. To unlock the layer, navigate to the layer settings and toggle the Lock Layer option off.