I can only sigh here, friend, prepare for a rant.
First, trust me, I am very much aware that some people will do whatever they heck they want without a care. Second, please understand that even though the art is uploaded on the internet it is still my intellectual property to which I own the rights to, that did not magically change when it got online. I have no real issue with my art being reuploaded. However. I want to know why, who, and where it ends up and then ensure it's properly credited. It is a matter of respecting the artist (in this case me) and showing common courtesy by ASKING first. This was further expanded on in my profile up until very recently (my core membership expired and I lost the extra box, I haven't had time to fix it up yet).
There is also the matter of there being a lot of commissioned pieces in my gallery. Though I own the art itself the subject matter belongs to someone else - someone who paid to have that art piece created. Also realize that reuploading art (especially without proper credit) doesn't actually help the original artist whatso-effin-ever most of the time. It just gives traffic/views/faves/comments to the reupload, very little trickles down to the original. It is sadly very common to have an original upload receive little attention while a reupload gets tenfold that. Copying/tracing/altering someone else's art is just plain disrespectful. As for stealing? People have grabbed and cashed in on my YCH and adopts more than once by uploading them elsewhere and claiming them as their own.
This sign is a sort of a "HEY, IF YOU FIND MY ART ELSEWHERE IT WAS PROBABLY NOT WITH PERMISSION" for those who cares to track down the original (I am regularly contacted by people informing me about YCH theft and reuploads). It also works as a reminder to those who are ignorant/thoughtless but still considerate of the artists feelings regarding the matter. It's not a matter of not wanting to be part of a global community. It is a matter of wanting others to show consideration to the artist for the time, effort, and skill that they have put into their art. Remember that it is a product that takes hours to create and only seconds to consume.
Edit: Woops, wrote "cropping" instead of "copying". Though cropping can be really disrespectful too, depending.