Is it a form of measurement? It's right next to the door, at eye hight. Here's a photo of it, in Vienna.
Are you talking about the kind you can see in these photos?
http://sbmp.provincia.venezia.it/mir/musei/portogruaro/citta08.jpg
They're called anchor plates, and they're connected to iron bars called tie-rods that run through the building. While some people think they're to hold the floors up, they're actually in there to hold the opposite walls together and keep them from bowing out. You see them on old buildings because we've since designed more advanced methods of reinforcement (like reinforced concrete, where you simply bake the iron bars right into the concrete). Since they were visible on the outside of the building, they're often given a decorative shape (like in the second photo), although the straight iron bar is just as common.
I am going to disagree with /u/Son_of_Kong.
I don't think those are anchor plates. I think that they are length standards. The shape, of them, with two "ears" sticking out at the ends looks a lot like this metre standard in Paris. Here's another one.
The height, that they are close together, parallel, and aligned at one end I would put forth as further evidence of this, and that they are on a public building which would have been community hub.
Finally, I don't think they're anchor plates because the height is wrong. That looks like stone construction, and I doubt that bowing would be a serious concern with this construction method, not even two meters off the ground. If you look at the photos they posted, you won't see the anchor plates any less than two and a half meters off the ground, usually more.
Again, I think they're length standards, but I'm not an expert, and I will gladly defer to anyone who is.
EDIT: Didn't even see /u/Broktok's post. :P
