The triquetra has been found on runestones in Northern Europe and on early Germanic coins. It presumably had pagan religious meaning and it bears a resemblance to the Valknut, a symbol associated with Odin.
G Scale Trains are usually referred to as Garden Trains since they are the largest of the model trains and are used outdoors as well as indoors.
A model that is 1:29 scale is one 29th the size of the actual train. Gauge refers to the size of the railroad track. This hobby is popular all over the world so the sizes are pretty standard regardless of where you are shopping.