From Longman Business Dictionary
endorseen·dorse /ɪnˈdɔːs-ˈdɔːrs/ (also indorse) verb [transitiveT]1LAW to sign a formal document for something that you own so that ownership changes to someone else 2BANKING to sign your name on the back of a cheque, a BILL OF EXCHANGE etc so that it can be paid to someone other than the person whose name is written on itThe bank could not confirm the endorsed signature so stolen cheques could be cashed long before anyone realised it.
3MARKETING if a well-known person endorses a product, they say in an advertisement how good they think it is. People will buy the product because they like or trust the person