The exact meaning of endorse can depend upon its context. For example:
"I endorse her candidacy." — support for a candidate
"I endorse the committee's recommendations." — support an idea
"She is paid a million dollars a year to endorse the company's products." — publicly support in return for payment
"She endorsed and deposited the check." — approved placing funds into a bank account by writing something like "for deposit" and signing the back of a check
With a clarity that was both surprising and somehow ominous he saw himself pulling the Camaro up to the drive-in window of the Boulder Bank the day before he had finished Fast Cars and dropping his check for four hundred and fifty dollars, made out to cash and endorsed on the back, into the tray (perhaps even then the guys in the sweatshops had been talking vacation?