The spionnetje is a typical Amsterdam thing. It's a rear mirror like spy-device people living at the upper floors use to see who is at the front door at street level.
The facades of the old Amsterdam houses are reflecting their history.
Pictures stones, ornaments, cramp-irons, skylights and gabels tell their own story.
When you are looking good and want to relax, pull up a bit of concrete and people watching is the preferred activity.