So how were houses identified in Amsterdam's medieval period? Well, you named them according to your name or profession, and then affixed a plaque with a design that identified that name to your house. Thus, if you couldn't read you needn't worry; you just found a house in the general area called "the crowned six-legged aardvark" or something and looked about half way up on the gable to find the plaque. Many still exist up there.
It wasn't until Napoleon came along that numbers were used to identify houses in Amsterdam.
Here some of the plaques are preserved in an Amsterdam cloister near the Historical Museum. 47 of these plaques are preserved here by bricking them into a wall, and over 650 have been preserved this way in all of Amsterdam. Keep an eye out.
For a more detailed description of architecture in Amsterdam, see Amsterdam Heritage.