As said, make sure you put a watermark on all of your design even if you are designing it for a client or just for inspiration. I am saying this because, I representing our company, have dealt several client and once a client rejected to pay and just tried to get the designs. But since it was watermarked I told him that I wont send him the Source files until he pays and then immediately he payed through Western Union.
Bottom Line : Watermark all files you've designed if you are publishing it.