A signal person can get a certification from a third party qualified evaluator. OSHA defines this as:

"an entity that, due to its independence and expertise, has demonstrated that it is competent in accurately assessing whether individuals meet the Qualification Requirements in this subpart for a signal person."

OSHA does not endorse any particular product or company, and does not detail any specifics as to what makes a"third party qualified evaluator" qualified to certify operators. The closest it gets to recommending a specific training product or company is in a letter of interpretation, where it states:

labor-management joint apprenticeship training programs that train and assess signal persons would typically meet the definition for a third-party qualified evaluator.

In the end, it is up to the employers best judgement to determine if the third party evaluator they have selected is an appropriately qualified party.

The employer can designate an employee to train and certify signal persons. They must be a "qualified evaluator, which OSHA defines as

"a person employed by the signal person's employer who has demonstrated that he/she is competent in accurately assessing whether individuals meet the Qualification Requirements in this subpart for a signal person."

Again, OSHA leaves it up to the employer to determine who meets this criteria. In it's letter of interpretation on the subject, OSHA reminds us that the employer is ultimately responsible for the training of their employees, regardless of where the training was completed.