I think you can only select one of the avatars they offer. If you mean signatures, that is a little different than avatars.
Edit: I just checked signatures and it says we cannot have images in them, yet I have seen people with something in their signature that looks like a picture or image.
If you're talking about in sigs, people are currently uploading them to external sites and using BBCode to place them in their sig.
That being said, I feel like its kind of cruel to the servers to have a big old image in your sig right now. These forums are going to be absolutely flooded, and having tons of images loading on every page is only going to make it that much worse.
Maybe those BBC codes should be blocked then. If the motive were to allow images in signatures, we would be able to.
This is skirting the system, which is exploiting.
I have a feeling that if the servers do get bogged down, disabling BBCode in sigs will probably be one of the first steps to alleviate some of the pressure
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