Maybe my opinion might upset you, but if people repost your gifs at other sites, don't complain too much or feel a sense of entitlement. Feel flattered that they share your awesome creations in the first place, and they mean not too much harm. However if they repost your work and claim "I made this!!!!1111" on Tumblr or anywhere else, then you have the right to file a complaint. When reposters share with no claims that they made this, it's fine and Twitter character limits credit space unfort.