I've been noticing that in almost every single house that I've gotten from iCad's tumblr recently has this weird thing on or near the mailbox. what does it mean?
Is it a bug or a glitch? will this cause issues in my game?

It might be a mailbox cover that was cloned from the end table and the CC wasn't included with the lot.

http://dramallamadingdang.tumblr.com/ See the mail box in the picture? (scroll down a bit) You can see the shelf. iCad has the mailbox cover by Windkeeper over it with a white recolour. The cover adds a shelf for sims to put the mail on. The cover is cloned from the table and you are missing the mesh so it shows for you as the table. You can grab the mesh off the Booty or TSR. http://www.thesimsresource.com/arti...helf/id/181696/ I use it on all my lots in game since I hate sims taking mail into the house and leaving it in some odd spot!

Edit: You can get all kinds of recolours for it, here's one set. http://modthesims.info/d/566206

If I remember correctly, the version from the booty was further hacked so that only mail can be placed on it. I think I read somewhere that some people had problems with the original where their sims would leave newspaper, coffee cups, etc. on it.

Have you sent iCad a message about it? If the mailbox cover mesh isn't packing with her lots, it would be nice to let her know so she's aware of that. (Try sending her an ask on her tumblr - she posts regularly there, as you probably already know.)

Edit: Now that I think about it, she usually puts meshes and recolors that didn't pack with the lot in a folder - that stuff needs to be added to your downloads before the lot is installed. Was there such a folder in any of the lot downloads?

I've looked back the original rar files and I've just realised that I deleted them thinking it was those mailbox recolours that I had in my game previously and it was hard to get rid off. My bad