Hello Joe, you as an artist must know at this point that every design has the risk to be copied by someone else and that my friend is the price to pay by every creator in this world even God has to deal whit the clonation, so dont woory to much because it is impossible (even when there are copyrihgt laws and all that stuff) to void that of happening, plus remember: imitation is a sign of admiration.
P.D How many of us designer could say that never had used someone elses designs???