Final answer:
'Signed' in the given sentence is a transitive verb as it is acting upon 'the autographs'. Transitive verbs have a subject and take one or more complements, commonly a direct object.
Step-by-step explanation:
The sentence given in the question has the structure: (subject)+(transitive verb)+(direct object). In this case, 'The baseball player' is the subject, 'signed' is the verb, and 'the autographs' is the direct object. Hence, 'signed' is functioning as a transitive verb as it is acting upon 'the autographs' in this sentence. Transitive verbs, by definition, have a subject and take one or more complements, one being the direct object which receives the action of the verb. On the other hand if no direct object is involved, then the verb would be called intransitive.
Learn more about Transitive Verb