Even if you're the sole owner, you cannot endorse business checks written out to your company in the same way that you endorse personal checks. This is because the payment belongs to the business.
Turn the check over. On the first line in the area marked "Endorse here," pen in the name of the business to which the check is written. If it was misspelled, write it with the mistake(s). Then write the official, legal name of the business.
Sign your legal name underneath the business name. If the business has another business owner, treasurer or partner who can legally endorse the check, he may sign it instead.
Write "For deposit only" or "For deposit to account number [the business bank account number]" on any checks that you send out to be deposited. This is called a restricted endorsement. Restricted endorsements prevent the check from being cashed out.