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.
Also see Model Railroad Scales for more info and history. The first model railways were not built to any particular scale and were more like toys than miniature representations of the full size prototype. Eventually, the authenticity of models grew and benefits of standardization became more obvious.