I have Googled it and checked several wiki....

Ok peoples, this is what forums are for.....

I have seen these strange markings on most buildings, none on any buildings we can own though, and none on some other peoples
structures. Look closely around peoples doors to find them, they are usually like a circle with some sort of design inside the circle.

Do any of you know what the meaning of these things is?

I have seen identical markings on several buildings and cannot draw the connection yet, If you can figure it out give me a shout here.

I noticed these aswell,possibly the house number or name in skyrim writing.

Just a guess though.

yep - seen them sunday in the evening and spent a thought about it. Didn't figure what they mean yet. :L
But the house number thing seems to be a good hint - maybe there isn't much about it.

Could also be some kind of "blessing" - I do come from germany and in the catholic parts of it most houses have written "blessings" on their doorframes.

decoration?

I have noticed this as-well, I have no idea what they mean....

I heard it has something to do with the Dark Brotherhood.

Not sure though.

It has to do with the Thieves Guild.

I also seen it... It is one on the ''pole'' to the right when you are on the small step up to Jorrvaskr... Very odd..

I think possibly it might have to with faction affiliations. Like, people who are in the thieves guild all live in houses that have
the same markings, and same for all the others. This may be so that you don't end up robbing or offing some one from a
guild you don't want to alienate. Like the blacksmith by the main gate in Whiterun, no marking on that building at all, so I
am guessing that you could murder and rob those people without hurting your affiliation with any guild. Probably why we
don't have markings on buildings we can own, because we don't need them. Other NPCs don't have markings on thier
buildings as well. There are a great many structures with the same markings too.

I still would like some sort of confirmation though, because this is just guess work on my part, the NPCs don't just come out
and say who they are aligned with like they do in other TES games. Like any one int he thieves guild would give you some
sort of nod to the grey fox or some such behaviours.

According to the guide, if these are the symbols you're talking about, then it's do to with the Thieves Guild. They're known as Shadowmarks and there are nine different ones which basically tell the player if an area is 'Safe' or 'Dangerous', if a house is protected by the guild and shouldn't be robbed, places worth stealing from and not worth stealing from and so on.

Dude I've totally seen these markings. They remind me of the runes from Assassin's Creed: Brotherhood. I don't want to read this thread because I don't want to find out what they are for yet though!

hahha, they are cool though. I love stuff like this.