Contacts

Yes, you have to sign it--or to be more accurate, if you don't sign, then unless you have a written employment contract already in place, guarantying or protecting your job and preventing termination, they could terminate you for not signing. But that's all they could do, since you did not sign the contract before taking the course: terminate you. So they can require you to sign in exchange for continued employment--BUT if the contract allows them to charge you even if you are terminated *not* for cause (i.e. terminated without warning or notice when when you did nothing wrong), then they could turn around and terminate you shortly after you sign, leaving you liable for the cost of the course. So a contract like this, which does not limit you to repaying only if you are fired "for cause" (or for wrongdoing) or resign makes you vulnerable, since you could sign, then lose your job, then be sued for the cost of the course under the contract. If the certification was not too expensive, it may well be worthwhile taking that risk; but if it was thousands of dollars, you may wish to consider whether it would be better to seek other employment then become liable for that amount.
If the contract limits repayment to resignation (under your control) or "for cause" firing (being fired for provable wrongdoing, which is rare and which you could dispute if you disagree--i.e. they might not win in court) the risk is considerbly less.