Your logo/design is your brand, the trick is to design one that is associated with your company, so that when seen, people know exactly who it is.
Copies, can be a form of flattery, however, if the other person/company should be responsible for an accident or some other form of mishap, you just might find yourself in a position of denial, risking your own livelyhood and reputation, you should alway's, alway's, protect your brand.
Regards
Rob