When someone writes you a check, you're the only person who can cash it or deposit it into your bank account. The only way around this is to "endorse" the check to somebody else, which essentially lets you pay that person with the check you received. Endorsing a check is easy enough, but getting it cashed is another matter. Some banks consider that endorsement a red flag for fraud and won't honor a check that's been signed over.
Verify If the Bank Will Allow it
There's nothing wrong with trying to sign over the check but if it goes against the receiving bank's policy, the bank simply will refuse to cash or deposit the check. Before you do anything, have both the check writer and the person you're signing the document over to call their respective banks and ask what's allowed. Some banks may be willing to accept checks that have been endorsed in favor of a third party; others will refuse for fear of fraud.
Sign the Check Over
Assuming it's permitted, endorsing a check is really simple. Just flip the check over and locate the endorsement area, which are the two or three lines beneath the words "endorse here" on the upper part of the check. Most checks say "do not write, stamp or sign below this line" beneath the endorsement area, and you shouldn't run into this area or the bank may refuse the check. Write "Pay to the order of [name of payee]" in the endorsement area and sign your name underneath that. This is known as a "special endorsement." Hand the check to your recipient. When he cashes the check, he will sign his name underneath and give it to his bank.
Go With the Recipient
Some banks won't accept checks with a special endorsement in case there's something fishy going on. That's because you've essentially made yourself a middle man, and the receiving bank cannot verify your identity or signature for fraud purposes. For all they know, you could have picked the check up in the street and forged a signature to match the name of the payee. One option is to go to the bank along with the recipient. Some banks will be happy to accept a specially endorsed check if you sign it over in front of the cashier and show your ID.
Where signing over the check is not an option, there are some other ways to pay the recipient. The easiest solution is to deposit the check into your bank account and write him a check yourself. You usually can get the first $200 of funds from a check within one business day so you shouldn't have to wait too long to access the money. Another alternative is to return the check to the person who wrote it and ask her to make a new check payable to the new recipient.